Social Networks of an Emergent Massively
Collaborative Creation Community
Case Study of Hatune Miku Movie on Nico Nico Douga

Masahiro Hamasaki1 and Hideaki Takeda2
1

AIST, Japan /JST CREST, 1-18-13 Sotokanda, Chiyoda-ku, Tokyo, Japanhamasaki@ni.aist.go.jp
2
National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo, Japan
takeda@nii.ac.jp

Abstract. The Web technology enables numerous people to collaborate
in creation. We designate it as massively collaborative creation via theWeb. It is coming to produce important activities such as Wikipedia andYahoo Answers. As an example of massively collaborative creation, we
particularly examine video development on Nico Nico Douga, which is avideo sharing website that is popular in Japan. We specifically examine
videos on Hatsune Miku, a version of a singing synthesizer application
software that has inspired not only song creation but also songwriting,illustration, and video editing. As described herein, creators interact tocreate new contents though their social network. As described in thispaper, we analyzed the process of developing thousands of videos basedon creators’ social networks. The purpose of this paper is to investigate
the relations among social networks and creation activities.

1

Introduction

The Web was created as a publishing platform, but it is increasingly becoming
a two-way communication platform for people. Thanks to the flexibility of theWeb, communications of various types have emerged. As a platform for communications, the Web presents various advantages over older systems. For example,
it eliminates the sense of distance because people at any place can mutually communicate. It supports massive interactive collaboration through large-scale BBS
and social tagging, which is impossible in real-world communication channels. It
also enables large-scale information sharing not only of texts but also of various
multimedia contents such as videos. This activity has already produced valuable
digital contents such as Wikipedia and Yahoo Answers, which could never havebeen born without the Web. We designate activities of this type as massively
collaborative creation by which a huge number of people mutually collaborate tocreate contents on the Web.
Massively collaborative creation on the Web has features that augment traditional collaborative creation; one is the style of participation. Vastly numerous
people are involved. For that reason alone, they often do not know each other.

II

Numerous evolved or inspired versions of a video can be created if a video explores a new idea or if it ”catches on”. Another difference is the digital reuse ofcontents. Some components of a work are reused in evolved or inspired versions.
For example, an image or sound in a video can be reused in a new version of thevideo. Consequently, digital work can be developed among people via the Web.
We are interested in the development of such digital works, particularly inthe process as it unfolds in a video-sharing website. We selected a video-sharing
website called Nico Nico Douga 3 , in which intense collaborative video creation is
occurring. We specifically address Hatsune Miku 4 , which is a version of singing
synthesizer application software that has inspired many people to produce various music, picture, and video compositions. The Hatsune Miku phenomenon isinteresting because different creators interact in projects: song creators, illustrators, and CG creators.
Some analyses of massively collaborative creation that have specifically elucidated relations among contents and creators have been described in the literature. Kittuer analyzed the effects of sharing roles on the quality of created
content [1]. Adamic analyzed a social network among questioners and helpers on
a QA site [2]. Results of these analyses contribute to our understanding of themassively collaborative creation activity of users. Our research was undertaken
to analyze types of massively collaborative creation that differ from those of earlier studies. In Wikipedia or Yahoo Answers, people create and modify sharedobjects; they often communicate with one another to coordinate their collaboration. However, on video sharing sites such as Nico Nico Douga and YouTube,people create their own contents freely; little explicit coordination takes place tocreate contents. Cheng et al. [3] investigated data of video posts and networks ofusers and videos on YouTube. Their analysis of large amounts of data is interesting, but the analysis is superficial: it does not address the semantics of video
creation. Halvey and Keane [4] made a similar analysis of YouTube.
The purpose of this paper is describe our investigation of the relation amongsocial networks and creation activities in massively collaborative creation communities. We adopted a method of social networking analysis as a basic method
to investigate the phenomenon. Applying social network analysis methods to
web contents has yielded important results for explicating the structure of interaction among people (see [5]). In our case, we investigate how different typesof creators interact to create new content through their social network.
The sections of this paper are organized as follows. We briefly describe thetarget of our analysis—Nico Nico Douga and Hatsune Miku—in Section 2. Subsequently, we explain our data extracted from the website and the preliminary
process for the analysis described in Section 3. We present the results of ouranalysis in Section 4 and summarize this report in Section 5.
This paper is an extended version of a preliminary report [6]. We herein describe results of the analysis in greater detail, in addition to new results obtainedusing different analyses.
34

http://www.nicovideo.jp/
http://www.crypton.co.jp/mp/pages/prod/vocaloid/cv01.jsp

III

Fig. 1. Screenshot of Nico Nico Douga. This video is an extremely popular video related
to Hatsune Miku.

2

Target2.1

Nico Nico Douga

Nico Nico Douga is the most popular video sharing website in Japan. Started
in December 2006, it now has more than 13.4 million users (July 2009); it has
published more than 2.8 million videos. Its basic service closely resembles thatof YouTube, but it includes some unique functions and has gathered many users
rapidly. The most interesting and unique function is the direct overlaying ofcomments on videos. A user can add comments about a specific playback time
at a specific position in the video (see Fig. 1), which gives people a sense of
sharing the viewing experience virtually. Furthermore, the creator can instantly
know which specific moment or specific scene is appreciated by a viewer. That
feedback inspires the original creator or other creators to produce new videos tomatch such effects.
In Nico Nico Douga, a popular category of video is a so-called MAD movie.
It is a fan-made video produced by combining video clips and sounds taken fromanime videos to create a new sense that differs from that of the original animatedproduction. It can be characterized as a mash-up style of video creation: a video
is created by mashing up existing video, sound, and image parts. Because of thatfeature of Nico Nico Douga, creators of MAD movies are mutually inspired andhave produced and uploaded many videos on Nico Nico Douga.
The key feature of a MAD movie is that the extracts that are used areoften taken from commercial anime programs. That feature has merit for people
because it is fun to view different versions of popular programs. Nevertheless,
it is problematic because it often engenders copyright violations. The birth anddevelopment of Hatsune Miku suggests a new direction to MAD movies. In
Hatsune Miku videos, extracts are not taken from commercial programs; instead,the community creates videos.

IV

Fig. 2. Reuse networks on Nico Nico Douga and Hatsune Miku. These pictures arevideos or illustrations on the Nico Nico Douga or web. Bold text shows the title andthat below is a handle name of a creator. Arrows among pictures indicate citations
from the source to the destination. A label on the arrows displays reused parts.

2.2

Hatsune Miku and Its Boom

Hatsune Miku developed by Crypton Future Media is a version of singing synthesizer applications called Vocaloid2; its uniqueness is that it adopted recorded vocals of a famous voice actress. Vocaloid2 developed by YAMAHA Corp. enables
users to synthesize songs that include singing by inputting lyrics and melody
on computers just like computer music. Amateur songwriters can publish theirsongs using Hatsune Miku. However, Hatsune Miku affected them more. They
regard Hatsune Miku as a pop singer so that they write and publish songs thatare suitable for her.
Moreover, a mascot image of Hatsune Miku has caught on. There is only asingle illustration of Hatsune Miku: it is printed on the software package. People
draw and post different illustrations of Hatsune Miku. Then people started tocreate videos, such as promotion videos for musicians, with such original songs
and drawings. Some people even create 3D models of Hatsune Miku and create
3D animation videos.
Figure ?? portrays an example of collaborative content creation on Hatsune
Miku. In this case, minato uploaded the video named ”Shooting star”. It consistsof an original song and one original illustration. That user created an original
song and tuned Hatsune Miku with it. Furthermore, he used one illustration
drawn by another creator when he created the video.
Another user, ussy, created a video resembling a promotion movie of Hatsune
Miku. It used the original song, a 3D model of Hatsune Miku and many pictures.
All had been created by other creators. He downloaded the video ”Shooting star”

Vand extracted music data. In addition, he downloaded the 3D polygon model
data and many pictures to create the video. This collaborative content creation
continued. A different user, F EDis, created a new video: a longer version of theussy’s video.
Then videos are created in the manner of MAD movies. Videos publishedalready are used as materials to create new videos. For example, one selects
lyrics and a melody from a video to refine songs; another picks up illustrations
from various videos to create scenes that are good for a new song. Fundamentally,
creators welcome the use of those materials because it indicates that their works
are valuable to others. As a result, many videos are created and published ascollaborative works.
The mixture of different creation types is very interesting. Hatsune Miku
gathered creators of different types: songwriters from the computer music field,
illustrators who come from ’doujinshi’— the self-published manga culture—andeven CG creators. Most are amateurs, but some are professionals. They are
stimulated by the work of others.
We found the following types of creations on Hatsune Miku.
– (a) Songwriting: Amateur songwriters are eager to promote their songs, but ittakes time and money to produce promotional tapes with professional singers.
Using Vocaloid, they can produce sound with vocalizations as computer music.
– (b) Song creation: It is not easy to make Hatsune Miku sing songs naturally.
Certain techniques are necessary to tune Hatsune Miku, but it is fun to tune thesoftware to create songs with nice singing voices. They vie with each other to createthem.
– (c) Illustration: The Hatsune Miku image is a typical anime character that attracts anime fans. Many fans are used to drawing their favorite characters by themselves. When doing so, they produce many different scenes and facial expressions.
They even produce different versions of the character, such as Hachune Miku (aninfantilized version of Hatsune Miku) and Yowane Haku (a fainthearted version).
Those with more expertise produce animations using such illustrations. Some evengenerate 3D models for Hatsune Miku and produce 3D animations.
– (d) Editing: There are so many Hatsune Miku videos that some people collectthem and produce summary videos, with ranking programs of Hatsune Miku
videos. That latter form is another kind of creation, but we exclude this type.
Videos of this type are, in fact, connected with other videos, irrespective of theircontent. Nevertheless, they are only related via data, such as those reflecting popularity.

We will analyze the creative activity on Hatsune Miku using the category ofcreation described above.

3

Data Collection

3.1

Data

In all, 36,709 videos had the tag ’Hatsune Miku’ on Nico Nico Douga (31 May
2008). From among them, we selected 7,138 videos that had been viewed moreVIthan 3,000 times as data for this study. We crawled their metadata during 1–
5 June 2008. The metadata include view times, the upload date, the uploader
name, tags, and a simple description. The most popular video had been viewed
4,425,208 times. The median number of views of the collected videos is 7,281.
These 7,138 videos were uploaded by 2,911 unique contributors 5 .
3.2

Category of Creation Activity

We presented four categories for activity related to Hatsune Miku movie creation: Songwriting, Song creation, Illustration, and Editing. In this section, we
present analyses of data based on these categories. The editing activity here is
excerpting and combining multiple videos. Therefore, it does not actually create
new contents of videos. For that reason, we used the former three categories. We
manually excluded 179 Editing videos that were responsible for viewing of the7,281 videos.
We classified videos and creators into creation categories automatically usingtags for videos. Tags on Nico Nico Douga include not only review or content
categories such as ’cool’, ’great’, and ’music’, but also kinds of creations: ’Originalsong’, ’Make It Sing’, and ’Make It Dance’.
We checked the top 50 popular tags and selected tags that are importantfor specific creation categories. Furthermore, we checked tags that have a highprobability of co-occurrence with selected tags. Then, we provided 24 tags tocategorize videos and creators. For example, if a video has the tag “Miku OriginalSong”, then we classify it as “Songwriting”. If a video has the tag “3D Hatsune
Miku Project”, then we classify it as an “Illustration”. A video can be classified
into more than one of these categories simultaneously if a video has tags ofdifferent categories.
We also determine the creator’s category by aggregating that person’s works.
A single creator is classified into multiple categories if the videos are classified
into more than a single category 6 .
Among the 2,911 creators, we were able to distinguish eight categories: threebasic categories, four others by variously combining the basic categories, and an
unknown category.
3.3

Reference Network

Each video has a title and a description written by the creator. The description
often includes hyperlinks to other videos that can reflect details of the video’s
creation. A customary practice on Nico Nico Douga is that a creator cites othervideos if a sound, image, or any part of another video is used. By tracing these5

On Nico Nico Douga, only the uploader is named. That person is not necessarily
the creator of the video. However, for this study, we regard an uploader as the video
creator.
6
Some videos cannot be categorized correctly using this method. We checked some
top-ranking videos and creators and corrected them manually.

VII

hyperlinks, we generated a reference network of videos. Among the collectedvideos, 4,585 videos include hyperlinks in the description; we obtained 12,507
links among videos.
We infer a relation between the creators of videos A and B when video A
has links to video B. Consequently, we generated a network among the creators.
This network has 2,920 nodes (creators) and 2,757 links (relations among thecreators). As described in this paper, we regard this network as a social networkof creators.

4
4.1

Results of Analyses
Reference Network Structure

The most cited video gathered 237 links. The video used an original song. These
well-cited videos have also collected many viewers. The most cited video was themost popular video. The correlation coefficient of the number of cited links andthe viewed times is 0.81. That coefficient indicates that these videos are reallyuser-generated contents because the creator’s behavior resembles the viewers’
behavior.
4.2

Category of Creation Activity

Figure ?? portrays the relation among creation categories. Table in Fig. ??
presents the number of creators and the number of in-links per creator by thesecategories. It might be readily apparent that the Songwriting and Song Creation
category attract many links, although Illustration does not. That fact indicatesthat Songwriting and Song Creation triggers creative activities. On the other
hand, Illustration acquires many creators. Illustration activity is good at attracting collaborators.
In this network of Fig. 3, the node size represents the number of creatorsof each category; the arc width shows the number of relations among creators.
We draw an arc among categories when the relations number is greater than
30. By following the links inversely, we can observe how the creative activity is
diffused among creators of different types. Songwriters and Song Creators are
the major source of the diffusion. Then Song Creators (only) and Illustrators
followed the diffusion. Illustrators were followed by themselves, which indicatesthat they diffuse Hatsune Miku in their community.
4.3

Community on Creators Network

In this section, we analyze the creators’ community. The term ”creators’ community” designates a tight group of nodes within a social network of creators.
We adopt Newman clustering [7] to detect such communities from the social
network of creators.
Newman clustering generated 83 clusters (communities) from the social network of creators. We especially investigated 10 clusters of which the size is greater

VIII

Fig. 3. Relation among creation categories. The left table presents creators of eachcategory. Therein, W signifies Songwriting, C means Songcreation, and I represents
Illustration. In addition, N and Ein respectively denote the number of creators andin-links.

Fig. 4. Structure of networks in the clusters.

than 50. Table 1 shows the parameters of these 10 clusters. Furthermore, Fig. 4
shows the structure of the networks in the largest four clusters.
In Table 1, Size denotes the number of creators in the cluster. Centralization
is an index of the centrality of a network in terms of degree [8]. In fact, χ2 showsa degree of bias of tags in the clusters. When creator A has a video tagged B,
we consider that creator A is tagged B. Then we can find the distribution ofcreators’ tags in the cluster.
The category of the key person (K-Cat) denotes the key person’s creative
category. We set a node that has the most links as a key person of a cluster.
However, we do not set a node as a key person if the number of links of thenode is less than 10 percent of all links of the cluster. In such a case, no key
person exists in the cluster. A category of majority (M-Cat) is the most popular
creative category of creators in the cluster.
Cluster 1 is the network whose center is the creator of the most famousvideo. The number of creators is 161. It is the biggest cluster on the network. The
central creator’s category is songwriting and the majority category is illustration.

IX
Table 1. Parameters of the biggest clusters. The K-Cat and M-Cat columns respectively show categories of key persons and the majority.
# Size Centralization (×10−3 ) χ2 K-Cat M-Cat
1 161
4.293
2130.5 W
I
2 144
0.080
1747.3
I
3 118
5.257
1921.0 I&C I, C
4 95
1.868
1857.7I
5 91
5.897
2799.9
I
I
6 90
7.055
2333.7 W&C
C
7 79
5.164
1942.8 W
C
8 56
3.012
1797.1
C,C&I
6.923
2079.6 W&C
C
9 55
10 51
4.000
1761.1I

Figure 4(a) shows the network of cluster 1. We can find the center node, which
has many links from other nodes. Cluster 2 is the second biggest cluster. No
centralized node exists on the network. In Fig. 4(b), some nodes exist which
gather some links, but the center of the network is not clear. Both Centralizationand χ2 are respectively lower than the values of other clusters. Cluster 3 shows
the network centered around the creator who produced the second popular video.
Creation categories are not the same, but the centralization and χ2 are similar.
Figure 4(c) shows a network that has a structure resembling that of Cluster 1;
it has a readily identifiable network center.
We observed that communities of two types exist from the viewpoint of network structure: a centralized community and non-centralized community. The
former includes clusters 1, 3, 5, and 6, in which there is only a single key personwith an extremely high number of in-links. The latter includes clusters 2 and 4,
which do not have key persons.
The key person in a community is often of the Songwriting category, whichindicates that Songwriting triggers creative activity. We also find that some communities have key persons with the Illustration category. In such communities,
new ideas are developed intensively such as new characterizations of Hatsune
Miku and a 3D modeling tool. Such communities contribute to widening theworld of Hatsune Miku and stimulating additional creative activities.
The results of the community-based analyses strengthen and refine the conclusion from the category-based analysis described in the previous subsection.
Collaboration of two types is identifiable. One type originates with Songwriting
creators, which involves Song Creation and Illustration creators. It represents
the birth of a creative idea and diffusion of a new topic. The other is collaboration among Illustration creators, where creators are mutually dependent. It isthe next phase within which diffusion takes place among Illustration creators.
Apart from the diffusion process, results show that centralization of the network and localization of the tag are mutually correlated. The correlation coefficient among centralization and χ2 is 0.63, which represents a strong positive correlation, meaning that a strongly centralized community tends to have

X

Fig. 5. Results of motif analyses with three social networks. The networks are as follows (where N and E respectively denote the number of nodes and links): (i) creators’
citation network on Nico Nico Douga (niconico N = 1454, E = 2339); (ii) a users’question and answer relationship network on the Wrestling community of Yahoo Answers (yahoo N = 9, 959, E = 56, 859); (iii) a friendship network of prison inmates(prison N = 67, E = 182).

community-specific tags that are used by many creators in the community andvice versa. In fact, tag analysis might be used to identify communities, which
can be quite beneficial because link identification is very costly and is often
impossible.
4.4

Analysis Network Motif

Motif analysis is a method used to investigate particular social dynamics using
small local patterns of a network [9]. The salient hypothesis of motif analysis isthat networks display certain patterns, termed ”network motifs,” at much higher
frequency than expected in randomized networks. We applied motif analysis to
our creators’ social network (Fig. 5). We also present the motifs of the twosocial networks for comparison. One is a social network of prison inmates [10],as analyzed by Milo. The other is a social network of a QA site (Yahoo Answers),
as analyzed by Adamic [2].
The normalized z-scores of 13 network motifs are presented in Fig. 5, themotif of which normalized z-score is high, meaning that it is a characteristic
pattern of the network. We used the motif analysis tool FANMOD 7 to carryout our motif analysis. In Fig. 5, our social network shows no triad 140 or 238.
The absence of triad 140 arises from the fact that our social network does notinclude such a local pattern. On the other hand, the absence of triad 238 occurs
from the fact that the random network has no such local pattern because thenumber of links to the number of nodes is too small.
Milo analyzed social networks among prison inmates, first year students, andother students. In addition, Adamic analyzed social networks of questioners andhelpers on a QA site. All of these networks show relationships among people;
however, they are networks of different types. The former is based on real-worldcommunication; the latter is based on online communication, especially questions
and answers. Our network is based on unique collaboration.
7

http://theinf1.informatik.uni-jena.de/ wernicke/motifs/

XI

Fig. 6. Results of motif analysis with social networks of three types. The networks are
as follows: (i) Sep. 2007 (N = 240, E = 296); (ii) Dec. 2007 (N = 976, E = 1450); (iii)
May 2008 (N = 1, 454, E = 2339).

Figure 5 shows that three results are fundamentally similar. It is clearly
different from other networks such as WWW [9]. However, each network has adifferent highest scored motif from the others. It is triad 36 in the case of our
network, triad 238 in the case of the prison network, and triad 38 in the QA site
network.
The prison network is based on real-world communication, although the others are based on online interaction. It is probably easier than for others to generate a complete graph (triad 238) in the network. Adamic interpreted the meaningof triad 38 on the QA site network as follows. In triad 38, one person was helpedby two others, but one helper has helped the other helper.
A star graph (triad 36) in our network is important in comparison to the othersocial networks. In this motif, a user is cited by two others; no relation exists
anymore, which indicates that a few popular creators attract many non-popular
creators.
Results show that the creators’ social network has characteristics resembling
those of other social networks. Furthermore, its remarkable characteristic is theexistence of popular nodes (trigger persons). How did such a network evolve?
The next question is how this characteristic is formed. We investigated the evolutionary nature of the network to answer the question. To investigate this point,
we generated networks in the specific periods and compared them. We split thewhole period into three: the first stage (to September 2007), the second stage(September–December 2007), and the third stage (December 2007 to the end).
Then we generated the network for the first stage, the network for the first andthe second stage, and the whole network (stages 1–3). We analyzed motifs ofthese networks (Fig. 6).
The characteristic triad (triad 36) is exaggerated as time passes. The initial
network is rather similar to the prison network, which indicates that the initialcollaboration is as close as that in the real world. The participants tend to citemutual work. However, the late participants do not. They are less cited andmerely cite the previous creators. It is interesting that the style of collaborationis shifted from a dense mode to a sparse mode, even in such a purely online
environment. It might be a hint indicating when and why the networks burst in
online environments.

XII

5

Conclusion

We have investigated how creators of different types interact in massively collaborative creative efforts. We extracted and analyzed the social networks of creators, revealing some interesting facts. Creators’ behavior is similar to audiences’
behavior. The creators’ network is large and sparse, and different categories ofcreators have different roles in evolving the network. Some communities in the
network are centralized, and some are not. Centralization of the network andlocalization of the tag are mutually correlated. Results also demonstrate thatthe style of collaboration shifts from a close one to a sparse one depending on
the evolutionary phase of the network.
Social media sites are expected to be interactive, but interactivity is not simple. As explained herein, creators of different types form interactions of different
types. It is also different depending on the evolution of the network. We shouldtake these points into account when designing new social media, particularly
those that support creative activities.

6

Acknowledgments

This research was partially supported by KAKENHI 20700146.

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