Isaku is a towering member of the Ittō-ryū who stands well over 6 feet tall, making him one of the group's most physically imposing fighters. What sets him apart, though, is that he doesn't actually carry weapons like the rest of his crew. Instead, he relies on heavy armor and a defensive fighting style—which makes sense given his role as Doa's constant companion and keeper.
Their partnership is basically the heart of his character. Doa's aggressive and impulsive, so Isaku's constantly apologizing for her antics, stopping her from killing people, and occasionally just picking her up and hauling her away from trouble. But it works: they've developed a genuinely complementary fighting dynamic where he plays defense while she handles the offense.
He's a pretty decent guy underneath it all—kindhearted and easygoing, though not exactly a genius. He comes from a Christian background (his father was a priest) and holds onto those values himself. Over time he also befriends Asano Rin and becomes part of a slightly wider circle.
Isaku goes through some serious trauma when he's literally cut in two during Habaki's experiments, but Doa manages to reassemble him. For a while after that he shares Manji's regenerative abilities, though they eventually fade away as time passes. It's one of the darker reminders of what happens to him throughout the story.
Content compiled by AnimeList.moe from publicly available sources.
