froggybaeks
[ loose inspo from the anti venom marvel character ]
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Yumi was born with Hypoplastic left heart syndrome, the left side of her heart critically underdeveloped. The first three years of her life were filled with surgery after surgery, the girl never being allowed to stay at her home for more than a couple weeks due to failure of the heart. Just before her fourth birthday, Yumi's parents are proposed a deal by a high ranking Yakuza member; they give their daughter up to them and they "fix" her, or she lives her final days, months, or years in pain.
The next day, Yumi is escorted to her new home with her single Finding Nemo plush and a note from her parents.
Chisaki Kai, the upcoming genius of the Yakuza, is instructed to use his Quirk to take apart Yumi's body and merge it with a symbiote one of their scientists manufactured. The process is a success - fusing the symbiote known as Anti Venom and Yumi together for the rest of her... their, lives.