Dorohedoro (Manga) Vol 01 (Mature)

In a city so dismal it's known only as "the Hole," a clan of sorcerers have been plucking people off the streets to use as guinea pigs for atrocious "experiments" in the black arts. In a dark alley, Nikaido found Caiman, a man with a reptile head and a bad case of amnesia. To undo the spell, they're hunting and killing the sorcerers in the Hole, hoping that eventually they'll kill the right one.

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