Eri was born with a mutated Quirk that allows her to "rewind" any person back to a previous state, but has little to no control over it. When this Quirk first manifested, she accidentally "rewound" her own father out of existence, causing Eri's mother to consider her to be cursed. Eri was then left with her grandfather, the former boss of the Eight Precepts of Death.
Overhaul later saw the potential of Eri's Quirk as a weapon to use against the Quirk-dependent society he loathes. After incapacitating his own boss, Overhaul repeatedly destroyed and recreated Eri with his Quirk to harvest her blood as the key material in the creation of his Quirk-Destroying Bullets, leaving her so traumatized that she has physically forgotten how to smile. But due to the efforts of a Hero operation led by Sir Nighteye, Eri was rescued from her prison by Izuku Midoriya and Mirio Togata, giving her the chance to be a normal girl for the first time in her life.
Powers and Stats
Origin: My Hero Academia
Speed: Below Average Human
Lifting Strength: Below Average
Striking Strength: Below Average Class
Durability: Below Average level
Range: Standard melee range to several meters with Rewind
Standard Equipment: None notable
Weaknesses: She has no control over her own Quirk and thus can harm others around her even if they are her allies. She is extremely traumatized by her experiences as Overhaul's prisoner, which can be used to manipulate her.
Rewind: Eri's Quirk has the ability to "rewind" individuals back to a previous state. The injured will return to peak condition and body modifications, even those as profound as Overhaul's Quirk, will be undone. Using this Quirk on a single person for a long-enough period of time will cause extreme pain that feels as though the target's own body were tearing itself apart before finally rewinding them out of existence completely. This Quirk first targets recent changes, allowing Izuku Midoriya to intentionally break his own limbs with One for All 100% to mitigate the effects of Eri's Quirk. However, the speed of the changes will also increase over time, as even Izuku's use of One for All 100% wasn't enough to save him until Eraserhead nullified Eri's Quirk with his own. Eri herself has little control over this Quirk, being able to activate it but not stop it, with its effects only ending after the target has been rewound out of existence, if the Quirk is nullified by another entity, or if Eri is killed.