Cosmo

A reanimated corpse serves as Cosmo's body, topped with spiky pink hair gathered into pigtails and held by red bands. Heart-shaped pupils, tinted somewhere between orange and yellow-red, fill her eyes, and the right one tends to dangle from its socket, apparently retractable enough for her to shift on her own. Much of her upper-right skull is gone, baring the brain, a length of which spills past her face and ends knotted into a small bow. Her outfit consists of a cropped, long-sleeved orange sweater, light blue shorts worn high on the waist, and pink sneakers.

On the outside she comes across as endlessly cheerful and untroubled, smiling through everything and uttering nothing but the word "Halloween" as she trails after Quanxi in unwavering devotion. Her real self surfaces only when she draws Santa Claus into her mind, where she speaks plainly and reveals a formal, level-headed nature far removed from her bubbly exterior.

There she shows herself detached and nearly free of feeling, unbothered even by the killing of her fellow lovers, which she treats as merely the way of things. The constant "Halloween" may be a side effect of her own ability turning back on her, yet unlike her victims she still follows speech, reasons clearly, and carries out orders without trouble.

Cosmo enters the story during the International Assassins arc as one of the lovers in Quanxi's circle, set beside Pingtsi, Long, and Tsugihagi, shadowing her leader and never voicing anything beyond "Halloween." After Santa Claus slaughters the others and threatens to make Quanxi into a doll, Quanxi orders Cosmo to unleash a full Halloween. Cosmo obliges, pulling Santa Claus telepathically into the library-like dimension of her mind.

There she names herself the Cosmos Fiend and explains, without any malice, that the assault is simply nature taking its course. Her gift, Total Understanding, forces a target to grasp the entire universe at once, hollowing them out until they can think or say nothing but "Halloween" until death. Santa Claus and all her dolls are left near-catatonic by it. The knowledge of everything lives permanently inside Cosmo's head, a near-omniscience she cannot truly wield, since her fiend body traps her in that same single word outside her mind-space. Despite her decisive help, Makima still beheads her along with Quanxi and Tsugihagi. Their corpses later pass into Public Safety custody, and Quanxi is said to have joined Special Division 7 on the promise of reclaiming her lost companions.