The past of Kuin Hachisuka is unknown, except that she worked for the Villain Factory, and she survives by taking possession of one host and changing to another when the former ceased to be useful to her. At one point, she met Tamao Oguro, daughter of Knuckleduster, and possessed her body, becoming her new host.
Since then, Kuin lived as a simple high school student, while doing assignments and jobs for the leader of the Villain Factory: In general, her job was to distribute Trigger through the streets, collect data from those that had been transformed into Instant Villains for the drug, and look for suitable candidates among these consumers to kidnap and transform into Next-Level Villains.
To survive, Kuin looked for a house and murdered his owners, using their corpses as food and hives for her bees, while she used the money from their credit cards to live, until the money ran out, at which point she left the place and looked for another family.
Kuin meets the Naruhata Vigilantes for the first time while walking with her classmates. Kuin notices Pop☆Step and asks Koichi Haimawari, who was with Pop☆Step, to take a photo of the two of them. After thanking them she runs back to her friends who were waiting for her. While she is admiring the photo a bee suddenly appears and disappears behind Kuin's eye-patch. She then runs away after claiming that she has to go to work.
Kuin takes her eye-patch off and releases a plethora of bees with strings containing the Trigger drug and they proceed to sting random citizens, turning them into monsters wreaking havoc in the city. The Instant Villains are quickly subdued by the Heroes. Kuin met up with Teruo Unagisawa while the attack was taking place and suddenly starts bleeding out of her eye because someone squashed one of her bees. Teruo and Kuin then continue to walk into a back alley.
Later as Kuin is shopping, her Trigger supplier calls and tells that she should pick her targets more carefully, focusing on those with strong wills and potential. That night, she offers Trigger to a drug addict and encourages him to use his enhanced power, which he does by trying to smash her, but she dodges the strike and continues encouraging him before leaping away.
The next day, Kuin is sitting in a cafe and on the phone with her supplier. She questions if they should take care of the three vigilantes that keep interfering, but the supplier points out that they receive real battle data without involving Heroes or the Police Force. After the call, Kuin is approached by a man, who asks if she is "Honey." Complimenting his appearance, she takes him by the hand and leads him outside.
She later allied with the vigilante Stendhal to get rid of some of the previous Instant Villains. Stendhal was gonna to kill Soga Kugizaki, but was stopped by the Naruhata Vigilantes. After being defeated by Knuckleduster and being enlightened by his words, Chizome understood that what he lacked was resolve. Kuin Hachisuka makes fun of him about his need for resolve, for which he throws a knife that sticks into her eye hidden by the patch. Giving her for dead, he walked away without realizing that Kuin blocked his attack. Despite this, Kuin decided not to retaliate, considering since he will makes things all the more interesting.
After this, Kuin continued with his job of distributing Trigger and search for candidates, being behind several incidents with Impromtu Villains, among them the incident with the Monster Cat that was about to cost the lives of Koichi and Makoto. On another occasion, she does not hesitate to use one of her classmates as a trap to kill Soga, when he was looking for her at Knuckleduster's request, although he manages to escape.
Her criminal routine continued until she heard about the Narufest party, a performance at the roof of Marukane Department Store with local artist and some guest heroes. Kuin Hachisuka thinks that she should unleash a surprise villain on the show. To do this, she decides to use Teruo Unagisawa, now transformed into a Next-Level Villain. The night of the show, she releases Teruo in the streets, causing panic among the passers-by, until Shota Aizawa appears and tries to stop Teruo. During the battle, Teruo unleash a large blast of electricity with his quirk that causes a blackout in the show on top of the department store.
Kuin Hachisuka sits atop a nearby roof, watching the events. She thinks about take advantage of the siytuation and pumping Trigger into the panicking audience at the show. But at that moment Knuckleduster appears behind her. He then calls her Tamao, and tells her to come home to her mother. At first, Kuin seems confused about that, but Knuckleduster tells her that he doesn't want to talk to the "Bee User", but that he wants to speak to his daughter, to who Kuin is using his body as host. Knuckleduster rushes towards her initiating a fight between them.
Kuin uses different stratagems to escape or defeat him, but all fail, and ends up being defeated when Knuckleduster ends the fight by hitting her in the chest with his Taser Knuckle, stopping her host's heart. Thanks to this, he manages to get Kuin’s swarm to leave his daughter's body. Using a small device, he extracts the queen bee, the real Kuin Hachisuka, from the hollow hole of her eye, and calls back the swarm with a pheromone & bomb combination device, which explodes, killing the queen bee and the swarm. Knuckleduster manages to resuscitate his daughter and save her.
However, without knowing it, a single bee survived and escape. Shortly after, a mysterious individual with a scar on his face notices the last of Kuin's bees shakily flying through the air past him. In a flash, he jumps up and catches the bee in a plastic capsule, commenting to himself about how "the many are reduced to one”.
Then, the mysterious man moves away from the place.