Chapter 4: I Opened the Book, Therefore.

is the fourth episode of Kamen Rider Saber. It features the only appearance of Saber Dragon Hedgehog and Saber Dragon Hedgehog Peter. This episode introduces Desast, leading to the arrival of Buster Genbu Jackun. Kento as Kamen Rider Espada briefly appears at the end of the episode.
==Synopsis==
Despite defeating the Megid, the city still hasn't reverted back to normal! Touma promises a worried Ryo Ogami who is missing his son Sora, that he will get him back! Ryo's feelings manifest towards Touma by saying "Do you understand what a parent is feeling?!" Despite this, Touma still promises to keep his word. Feeling frustrated and full of intense emotions, Ryo seeks to inform the sage of what has occurred. The case of the Megid is still a mystery, and just where did these people disappear to?! Touma and Rintaro think this situation over carefully, as Mei, who feels responsibility for what happened, suddenly makes a rash decision...!
==Plot==
==Cast==
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*: (Uncredited)
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*Narrator, Seiken Swordriver, Wonder Ride Books: 
*Seiken Swordriver: 
===Guest Cast===
*: https://twitter.com/saikireika/status/1309417667464314880
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===Suit Actors===
*Kamen Rider Saber: 
*Kamen Rider Blades: 
*Kamen Rider Espada: 
*Kamen Rider Buster: 
*Kamen Rider Calibur: 
*Desast: 
*Hanzaki Megid: 
==Forms and Collectibles Used==
===Wonder Ride Books===
*Book Used:
**Saber
***Brave Dragon, Needle Hedgehog, Peter Fantasista
**Blades
***Lion Senki, Peter Fantasista
**Espada
***Lamp Do Alangina
**Buster
***Genbu Shinwa, Jackun to Domamenoki
**Calibur
***Jaaku Dragon
*Form Used:
**Saber
***Dragon Hedgehog, Dragon Hedgehog Peter, Brave Dragon
**Blades
***Lion Fantasista, Lion Senki
**Espada
***Lamp Do Alangina
**Buster
***Genbu Shinwa, Genbu Jackun
**Calibur
***Jaaku Dragon
==Errors==
*to be added
==Notes==
*As part of Super Hero Time, this episode aired alongside episode 25, .
**Coincidentally, both episodes featured a new recurring villain.
*Closing Screen Wonder Ride Books
**Kamen Riders: Saber
**Wonder Ride Books: Needle Hedgehog
*Wonder World Text Translation Page
**Wonder Ride Books: Needle Hedgehog, Jackun-to-Domanenoki
Saber EP04 Hedgehog Eyecatch B.png|Needle Hedgehog (Story Page)
Saber EP04 Jackun Eyecatch B.png|Jackun-to-Domanenoki (Story Page)
*Count at episode end
**Wonder Ride Books in Saber's possession: Brave Dragon, Needle Hedgehog, Peter Fantasista, Diagospeedy
**Wonder Ride Books in Blades's possession: Lion Senki, Book Gate
**Wonder Ride Books in Espada's possession: Lamp do Alangina
**Wonder Ride Books in Buster's possession: Genbu Shinwa, Jackun to Domamenoki, Storm Eagle
**Wonder Ride Books in Calibur's possession: Jaaku Dragon
*This episode marks the first time any Rider has directly transformed from their human state using two books.
*This episode marks the first time a Rider has transformed using three books.
*This also marks the first time that Riders have dueled each other, specifically Saber, Blades, and Espada against Calibur.
*This episode marks the debut of Storm Eagle and Needle Hedgehog Wonder Ride Books.
*This also
==External links==
*TV Asahi's official episode guide for 本を開いた、それゆえに。
*KR Official's official episode guide for 本を開いた、それゆえに。
*JAE's official episode guide for 本を開いた、それゆえに。
==References==
Category:New Kamen Rider Episode
Category:New Form Episode