Who is this?

Himiko Toga is a major supporting character and a member of the League of Villains, affiliated with the Vanguard Action Squad. Himiko and the rest of her team serve as the main antagonists of the Forest Training Camp Arc, and she is also featured as an antagonist during the Provisional Hero License Exam Arc and the Shie Hassaikai Arc.  

Himiko is a very cheerful girl, to the point of smiling even after having presumably killed someone, displaying apparent sadistic tendencies. This continues even when danger is imminent, as when Tomura Shigaraki was about to attack her, but it tends to stop when she is bored or annoyed. Himiko is frequently seen blushing seemingly out of excitement rather than embarrassment, giving her a permanent look of what appears to be lovesickness on her face. However, she has shown that she can easily be embarrassed, such as when she thinks people are coming on to her, or when she is naked when copying clothes of the people she has transformed into.

Quirk

Transform: Himiko's Quirk grants her the ability to take on the complete physical appearance of another individual by ingesting their blood, including their voice. She also can copy and change their clothes, getting naked before doing this as her regular clothes would overlap her disguise. She can shift between multiple disguises if she has consumed different people's blood.  

Video Reference

https://www.youtube.com/watch?v=E1SuBWu4CSQ