Jinmen manifests as a massive, bipedal turtle demon clad in maroon skin and a green shell, with powerfully built limbs. His eyes feature yellow sclera and black irises. His shell bears the conscious faces of his preserved victims, serving as both a psychological weapon and a physical shield in battle.

He exhibits extreme sadism, reveling in his victims' torment. Jinmen manipulates foes by exploiting their emotional ties to faces on his shell, like Sachiko, childhood friend of protagonist Akira Fudo. When overpowered, he displays cowardice, begging for mercy and bargaining with the lives adorning his shell.

His abilities include limb extension for grappling and heated palms that inflict burns. He achieves flight by retracting limbs and expelling jets of hot air or flame from his shell. After prolonged time in Hell, he gains additional powers like lightning projection and high-speed spinning during flight.

In the OVA narrative, Jinmen massacres train passengers, including Sachiko. He lures Akira to a park by displaying Sachiko's face on his shell, taunting Akira about her suffering during their fight. Responding to Sachiko's plea for death, Akira kills her to end her torment. Jinmen attempts to flee but is torn in half when Akira rips off his shell, killing him and the remaining victims.

In broader Devilman media, Jinmen's story varies:
- The original manga depicts him killing Miki Makimura's niece Sachiko.
- *Devilman Crybaby* reimagines him possessing Akira's father, resulting in both parents' deaths.
- An unrelated horror manga titled *Jinmen* features animals with human faces seeking revenge against humanity, sharing no connection to this character.