Sword Gai
Japanese title: 『ソードガイ 装刀凱』3DCGプロモーションムービー
Type: ONA
Episodes: 1
Source: Manga
Genres: Action, Supernatural
Studios: Digital Frontier
Duration: 1 min
Rating: R - 17+ (violence & profanity)

A promotional video for the manga.

The story revolves around Gai, who was born beside a woman who met her death in a forest. He was adopted by the swordsmith Amon. A few years later, Gai becomes Amon's apprentice, and during the forging of a sword, he loses his right arm. To help him, Amon crushes the demon sword Shiryū (lit. Death Dragon) to form it into his replacement right arm. He then is able to fuse with the weapon on his arm, and fights against his enemies.

(Source: ANN)