Ayumi is unsociable, cool and always aware in herself. She says that she don't like violence and always drags in Mio's plans with hesitation.

Spoiler

Actually she is loups-garous ("werewolf"). Than someone becomes danger to her life or life of someone she cherish Ayumi turns to real killing machine that could end someones life without hesitation. Mainly uses knife for slaying. Probably becomes slightly stronger in "werewolf mode"