Koza

Koza turns up out of Mugen's past, in the rough island world he left behind long before Fuu and Jin ever knew him. She's sharp-tongued and guarded, someone who remembers exactly who he used to be, and she isn't impressed by the swordsman he's become.

She works because she refuses to be just a plot device unlocking Mugen's backstory — Ai Maeda gives her a flinty, unsentimental voice that treats old wounds as facts rather than melodrama. Through her the show lets Mugen's past intrude on the present without softening him, and without asking us to pity him either.