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This article contains plot details about the source material.
Kaisuke ( 甲斐 Kai) is a junior member of The Capsules, 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 very few living residents of Neo-Tokyo (along with Kaneda, Kei and Colonel Shikishima).
Kaisuke is a very short boy of less than average height, and has a brown, spiky hair. 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, combined with regular brown pants. His gloves are long and red.
Kaisuke is the mechanic of the group, best shown when he was trying to charge the battery on his motorcycle using jumper cables from a laser gun battery (although he accidentally set his bike on fire during the process). As well as the other members of the Capsules, he has little to no respect for authority figures.
Despite this, he is one of the softer, less volatile members of the group and shows a lot of care and responsibility. Deeply emotional, he is shown to be bursting in tears when he sees Kaneda surviving the explosion of Neo-Tokyo, and shown 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, playing the role of Kaneda's sidekick for much of the story. He develops a crush on Kei during their time together, which was cut entirely from the film adaptation.
甲斐 possibly means "worthwhile."