Cosmina was one of the members of the Empire's Secret Police, Wild Hunt. She was a singer equipped with a microphone; after being critically injured, she was modified by fellow Wild Hunt member Dorothea into a large monstrous creature.
Cosmina was a young woman with bob-style haircut and bunny ears accessory on her head. She wore a mini dress, a collar and matching wristbands, boots and a pair of glasses. Prior to her introduction, Cosmina wore a hooded jacket.
Cosmina loved putting on a show for her opponents while killing them, singing and striking stage-like poses with a cheerful smile and showing no remorse for her actions. She was the only Wild Hunt member to genuinely care about her comrades, as seen when she showed concern for Champ (whom she also affectionately called "Champie"), and when she didn't attack Izou and Dorothea even after her transformation into a monster.
She was also severely perverted. When Enshin kicked her for not "sharing enemies to kill," she had no problem flaunting her underwear while telling him she'd take care of him later; this happened multiple times, with Cosmina seemingly enjoying it. During the incident of the Umatora Theater, she took part in the mass rape, taking "all the pretty boys". She was similarly infatuated with Run and even after the Jaeger's deception of Wild Hunt became apparent, she only claimed to the suspicious Enshin that he was being "jealous" and "insecure"; later, when Run was near death, Cosmina saw nothing wrong with "having fun" with him.
After being transformed into a Danger Beast hybrid, Cosmina hungers for human flesh to eat in order to grow stronger but still held old memories of her former self that prevents her from attacking her comrades as noted by Izou and Dorothea.
Some time before the start of the series, Cosmina lived in the Western Country and, due to her voice that could manipulate people, was branded as a witch. This led to her house being set on fire, killing her entire family. Cosmina was the only survivor, the loss and trauma driving her into insanity.
Cosmina was then seen again when the Wild Hunt was introduced to Honest. She displayed her Teigu's power, which produced devastating, bone-shattering sound waves. During the investigation at the Umatora Theater, Cosmina gladly took part in mass rape, taking all "pretty boys." She was present during all other affairs of her group.
Later, as Run visited the Wild Hunt HQ, she greeted and flirted with him; however, after Run lured out Champ with the intent to avenge his students' death, Cosmina and Enshin followed them in suspicion.
The two were intercepted by Kurome and her corpse puppets; Cosmina managed to destroy two Danger Beast puppets using her Teigu's maximum power. After Champ's attack left Run fatally injured, Cosmina attempted to rape him; however, this distraction caused her to be shot by Mine from a distance.
Close to death, she was picked up by Dorothea, and was put in a cryogenic tube at the newly established workshop in the Capital. However, due to being left in a near-death state for a prolonged time, Cosmina received permanent brain damage; later, as a result of Dorothea's experiments, Cosmina was mutated into a monstrous creature.
She, along with Dorothea and Izou, attacked a Revolutionary Army outpost, slaughtering and consuming a large amount of soldiers there. When Night Raid arrived to fight them, Cosmina was cut by Akame but recovered from the poison thanks to the Philosopher's Stone embedded in her chest and then confronted Tatsumi, who killed her by bifurcation.
Equipment and Skills
According to Syura, her voice was capable of manipulating people; she appears to possess great vitality which greatly surprised Dorothea, a seasoned alchemist.
Cosmina used the Teigu, Heavy Pressure, which enabled her to unleash devastating, super-sonic sound waves, pulverizing and destroying the bones of her victims.