Kokubunji Koyori

Koyori is a friend of Komugi and works with her as a model and cosplayer. However, from time to time, Koyori will lose consciousness and transform into Magical Maid Koyori, her evil form. Koyori will then infect innocent people with viruses. She could be considered Komugi's rival. She often gets frustrated at being constantly defeated by Komugi and Mugimaru. After a time, she will revert to her good form again with no memory of anything she did in her evil form.

(Source: Wikipedia)