This article contains plot details about the source material.
Kai ( 甲斐 Kai) is a junior member of Kaneda's Gang, and the youngest one in the group after Tetsuo Shima. He serves as a supporting character in the anime film. By the end of the story, he is one the few surviving characters, and possibly one of the few living residents of Neo-Tokyo.
Kai is a boy of less than average height, and has brown hair that flows to the left. Unlike other members, who either dress in various vests and jackets, he wears a simple green jacket with a light-green tucked shirt and a red tie.
Kai seems to be the mechanic of the group, shown when he was trying to charge a laser gun battery using jumper cables attached to a running motorcycle. As well as the other members of Kaneda's Gang, he has little to no respect for authority figures.
Despite this Kai is one of the softer, child-like, less volatile members of the group. He shows a lot of care and responsibility. Deeply emotional, he is shown mourning Kaneda in the last half of the film before finding him after the event. He showed genuine concern about Tetsuo despite the fact he already killed Yamagata in front of him.
Kai is a much more prominent character in the manga, although is absent from volumes 2 and 3. He plays the role of Kaneda's sidekick. he informs him about Tetsuo's activities after they meet again after the destruction of Neo Tokyo.
- Kai is referred to as "Kaisuke" in early sources, particularly the previous English translations of the manga.