Dorohedoro, Vol. 1

Turned into a man with a reptile head by a sorcerer, Caiman must hunt down the sorcerers in the Hole, and regain his identity.
Caiman was not lucky. A sorcerer cursed him with a reptile head and left him with no memory of his life before the transformation. Adding to the mystery, there's a spectre of a man living inside him. But Caiman has one key advantage: he's now completely immune to magic. Along with his best friend, Nikaido, Caiman is hunting down sorcerers in the Hole, searching for the one who can undo his curse and killing the rest. But when En, the head Sorcerer, of the sorcerers, gets word of a lizard-man slaughtering sorcerers, he sends a crew of "cleaners" into the Hole, igniting a war between two worlds.