Manji is immortal but trapped in a curse that demands blood to survive, so every kill gets him closer to death instead of away from it. The genius isn't the premise, it's that Rin's arrival forces him to want something other than his own ending for the first time in decades, and that collision between a man built for slaughter and a person worth staying alive for is the entire show. The violence isn't decoration here. It's the language Manji speaks because he's never learned another one, and watching him try anyway is where the tragedy lives.

Manji is a swordsman in feudal Japan, infamous as the Hundred Man Killer and cursed with immortality by bloodworms that heal almost any wound. The nun Yaobikuni placed them in his body. To atone and win back his mortality, he vows to slay one thousand evil men, and she promises to lift the curse if he succeeds. Soon after, he meets Rin Asano, a 16-year-old girl seeking revenge on the Ittou-ryu, the swordmasters who killed her parents. He refuses her at first, but seeing his late sister in her, he agrees to guard her. Their journey is a bloody action tale of vengeance and redemption.