Li Sei commands Chintou Pass, the strategic checkpoint between Chouka and the northern Yin provinces—and he's the father of Nataku.
He's got an interesting backstory: he trained in the senning world years ago but kept failing, which meant he never managed to get a paopei. He eventually went back for round two and finally got one—Reiroutou, this obelisk-shaped weapon that fires at ghosts and works by channeling the user's own grudge to curse someone to death.
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