Eri is a small, young girl with pale blue-grey hair and red eyes. She has a small horn on the upper-right side of her head, this horn appears to grow in conjunction with her Rewind Quirk. Due to Overhaul's experiments of disassembling and reassembling her, she has a number of scars across her arms.
Eri is a timid and innocent little girl and as such, she wants no part in Overhaul's horrid plans. During her childhood with the Shie Hassaikai, she repeatedly tried to resist and escape her captivity only to be stopped and recaptured every time, leading her to accept her fate as a prisoner. Having mentally accustomed to this treatment, Eri does not cry or scream when somebody intends to harm her. Instead she remains silent while trembling in fear, knowing that she doesn't have a choice but to accept whatever will happen to her. After remembering Izuku Midoriya helping her up and holding onto her, she cried upon realizing that his act was out of genuine kindness.
Rewind: Eri's Quirk allows her to rewind the state of a living being, this includes her reverting a person's age and, as shown with her father, being able to rewind a person out of existence. She is able to use this power to revert injuries as well as allow Midoriya to use One For All: Full Cowl - 100% by preventing the power from harming him. Aizawa also remarks that Rewind could be used to help restore Mirio's Quirk. When active, an unknown energy flows from the horn on Eri's head. This Quirk was not present in Eri's blood line and is instead a result of an extremely rare genetic mutation.

Due to her young age, Eri has no control over her Quirk and fears it harming others. It's dangerous power makes it difficult to train, given that it can only be used on living beings. After training with the help of Aizawa, Eri was able to use Rewind with success by practicing on bugs and lizards. At Mirio's request, Eri successfully restored his Quirk.
Also Shinsuo is my brother.
Eil_was_found it my BFF