Jimmy appears in the final issue of the comic, following Johnny's death and rebirth. Calling himself by the self-given nicknames "Mmy" and "Darkness," he appears on Johnny's doorstep and introduces himself as Nny's fan and devotee. Jimmy has a strikingly similar appearance to Johnny, much of which, it is implied, is an affectation intended to emulate the title character: he sports Nny's original haircut, skinny body, and very similar clothes (though his shirt has a striped torso and solid sleeves, the oppisite of Nny's). It seems that he is younger than Nny. He is the only known person successful in tracking down Johnny's home of his own volition.
Jimmy informs Johnny that his interest in the latter's "work" began when he witnessed the destruction of a "Taco Hell" outlet by Johnny from a "CD Cesspool" store across the street. At that point, he decided to mimic Johnny's actions, to the extent of assembling a suitcase full of blades and surgical equipment. He gleefully recounts to Nny the murders he has committed to date—his first grade teacher, and a girl who resembled someone who bullied him in high school. He also admits, with relish, that he raped his second victim in an alley behind a mall before killing her (this incident was referred to earlier in the story and blamed on Johnny). As Nny grows visibly more and more disgusted with Jimmy's presence, Jimmy indicates that he would like to team up with Johnny and continue their mutual killing spree.
However, Jimmy's attempts at mimicking Johnny are an abomination in Nny's eyes, though Nny acknowledges that Jimmy's sociopathy "is a more reasonable facsimile of [Johnny's] own work than [Johnny would] like to admit." Despite being given several chances to simply leave, Jimmy persists, and Nny proceeds to kill him.
During the torture that follows, Johnny makes particular reference to the rape of the girl, which he finds unforgivable, stating that he himself would never do such a thing, as he considers even basic physical contact with people to be distasteful (at the time of the issue anyway), and that he considers such an act to be giving in to emotion, something else which he also by this time finds abhorrent. He also speaks at length on the subject of his distaste at being imitated at all. As Johnny is speaking, Jimmy is vivisected with several hooks, opening his torso. Johnny replies to Jimmy's final statement that he is "just like" Nny by smashing a sledgehammer into Jimmy's open chest cavity and stating, "I don't like myself much."
It is generally assumed that Jimmy represents a particular breed of JTHM fan that seeks to emulate Johnny, Vasquez's style, and/or even Vasquez himself, as Nny is depicted as being particularly distressed at the fact that that Jimmy's mimicry may be more accurate than he would prefer to believe. The idea that Jimmy may be a parody of a portion of JTHM's fanbase is also indicated by the facts that Jimmy's speech and mannerisms are like that of a stereotypical teenager, and that he doesn't seem to understand the little bit of underlying reason behind Johnny's acts of murder. At one point, Jimmy suggests that "[Johnny] should kill more, and talk less," which may refer to fan reactions to Johnny's monologues and existential angst in later installments of the series.