Yakumo Fujii

He became Pai Ayanokoji's Wu and companion when a rampaging Takuhi, Pai's demon friend, fatally wounded him. Before he could die, Pai merged his soul with her own, transforming him into a Wu, which in turn made him immortal as long as Pai lives. He can feel pain but he won't die. He will regenerate from any wound, no matter how severe.