Eri (壊理) is a young girl that Chisaki claims to be the father of and is the key source of his operation to manufacture Quirk Destroying Bullets.
Eri is a child with bandages all over her body. She wears a white short sleeve dress and has a small horn on the right side of her forehead and has long, choppy, unkempt hair.
Eri is a frightened and innocent little girl who doesn't want to take part in Chisaki's plans. Because of this, Chisaki considers her a "troublemaker".
Her relationship with Chisaki and the Eight Percepts suggest that she has never felt affection in her life, since she claimed up until now, Izuku's touch was the first time she felt kindness, which overwhelmed her.
Eri is however willing to let herself go with Chisaki in order to protect those that help her.
Eri was running down an alley away from Chisaki, mentally chanting she had enough of her treatment and wishing someone would save her. She bumps into Izuku and Chisaki catches up to them.
Quirk and Abilities
Deterioration Quirk: Eri's blood is able to attack an individual's Quirk and stop its activation.
This ability within her DNA makes Eri an important part to Chisaki's plans. Supposedly, he is using her blood to stop the activation of Quirks in order to control society through fear (much like how All For One controlled people by taking away their Quirks) and using that as a means of destroying justice.
Due to the unknown nature and lack of information so far about this ability, much of Eri's abilities remain mysterious. It is unknown if this is her Quirk, another form of mutation or even how this negation ability works.
Similar to how he treats his members, Chisaki only values Eri for her use. However with certain members, like Chronostasis, Chisaki values Eri enough not to consider her to be disposable.
Eri is terrified of Chisaki; her fear of Overhaul is strong enough to make her not disobey him when he gets serious.
He was the first person she bumped into when running away from Chisaki. She tearfully pleaded for him to not leave her alone with Chisaki and to help her. Izuku was suspicious of Eri's unnatural treatment. Even though he was instructed to remain covert around Chisaki and despite the interventions of Mirio and Chisaki's rebuttals, Izuku desired to protect Eri.
When Chisaki took off his glove and revealed his killer intent, Eri immediately went back to him. Izuku was shocked and confused by her behavior. He wanted to reach out to her but was held back by Mirio. He could only look on in worry as she was taken away. After that event, Izuku's focus becomes clouded by many distracting revelations and concerns. The majority of his concerns have been cleared, but his concern for Eri remained.
When Izuku learnt the origin of the Quirk attacking darts and its connection to Eri, he was devastated and felt immense regret for not rescuing her when he had the chance. He felt responsible for Eri's situation and resolved to rescue Eri no matter what.
For Eri, meeting Izuku left a profound effect on her. When he held her protectively, it was the first time she felt kindness from anyone. She willingly give up herself to protect Izuku from Chisaki when he was about to attack. This kindness she felt from him was strong and left an emotional impact on her, she wrapped a pillow around her head while remembering how it felt when Izuku touched her and tearfully overwhelmed by his actions.