Nail Fiend

The Nail Fiend wears the office-worker shirt and jacket common to Public Safety personnel. Its standout trait is a face cleaved straight down the middle. The right side gapes open, baring brain tissue riddled with nails where other organs ought to be, and a pronounced split runs across the right cheek, perhaps a remnant of whatever killed the original body. A long fringe drapes the left half down to the nose, and the medium-length hair at the back flares outward. The build reads as androgynous: the trousers ride high at the waist as worn by Public Safety women like Himeno and Makima, yet the chest and shoulders are broadly masculine, and a prominent Adam's apple rounds out the ambiguity. A hammer is forever in hand, which it brings to bear in combat.

Much like Katana Man, the Nail Fiend professes a moral code, faulting the Church for drilling children into soldiers rather than letting them learn, and scolding Yoru as rude for booting Fami aside. That principle sits beside a brutal streak, however: the Fiend once battered a child it claimed to safeguard merely for answering impolitely, surely scarring the very innocent it posed to protect. The protective instinct is genuine all the same, since its horror at watching children who carried Fire Devil contracts be slaughtered is what finally turned it against Public Safety. Theatrical and merry, it strikes poses mid-battle, laces its movements with flips and slides, and props a hand on its hip while chatting. It peppers its speech with pet names, dubbing the Church's young ones moppets and dears, and meets danger with breezy unconcern. In the Japanese text it refers to itself in unisex terms. It also shows attraction toward men, once lying beside a sleeping Denji, though his crudeness swiftly snuffs out that interest.

The Fiend began as an unremarkable human who died under unclear circumstances; the Nail Devil then claimed the corpse, and Public Safety took the resulting being into its ranks, most likely after Makima's death. As a Fiend it cannot forge contracts, and its might falls short of its former devil shape, though it keeps the baseline devil traits. It moves at blistering speed, able to disarm a whole squad of gunmen while slipping past every bullet, and swings its hammer hard enough to embed nails deep in concrete from a distance.

The Chainsaw Man Church arc opens with Public Safety dispatching Katana Man alongside the Nail Fiend to storm the Church's headquarters once Quanxi has captured the Weapons. The pair seize the younger members and rebuke the cult for arming minors instead of schooling them. When a restrained student answers a demand to study with indifference, the Fiend strikes him bloody, and the duo soon brace themselves as the children warp into imitation Chainsaw Devils through their Fire Devil pacts.

By the Aging Devil arc, the two guard the Tokyo Devil Detention Center and set an ambush for Asa and Fami's party. After several missed strikes at Fami, the Fiend admits it has grown weary of butchering children, branding the work cartoonishly evil, and agrees to a truce so the group can pursue Chainsaw Man. They discover his dismembered body packed into boxes, and the revelation that he is Denji stuns Asa. Quanxi then attacks on Takagi's orders, overpowering the Fiend despite its endurance through repeated stab wounds. After the group escapes to Fami's apartment, the Nail Fiend helps watch over the sleeping Denji, remarking on how cute he looks, and later stays behind with Seigi to mind the place.