Jinmen is a demon whose body is covered in a turtle-like shell, except the shell itself is made up of human faces—every person he's ever consumed. The twist is that his victims don't actually die. They stay alive and conscious, trapped as part of him. It's genuinely disturbing.
Which person Jinmen devours depends on the version. In the manga, it's Sachiko, Miki's niece. The first OVA has him going after Akira's mother instead. Then Devilman Crybaby takes it further by making Jinmen Akira's father, who's also consumed Akira's mother—raising the emotional stakes considerably.
Design-wise, Jinmen started out pretty faithful to his manga look in the first OVA, but they redesigned him for the second one. Interestingly, his fight with Akira in Cyborg 009 VS Devilman is probably the most accurate adaptation of how their battle actually goes down in the source material.
Content compiled by AnimeList.moe from publicly available sources.
