Beast

Beast is an alternate Tohka Yatogami from a parallel world where events played out very differently from the world where the main story occurs. Just like the original Tohka, she met Shido Itsuka and was saved by him. However, in this world Shido died, causing Tohka to fall beyond the abyss of despair. In the process, she completely lost her sense of self, attacking everything and killing the other Spirits in the process.