Seiren

A student of the Night Class, she is Kaname's unofficial bodyguard. She is usually the first to defend Kaname from anyone she regards as a threat. For example, she barely refrains from killing Zero when he points a gun at Kaname for comparing Zero to a level-E. It seems she also acts as a spy for Kaname. from http://vampireknight.wikia.com/wiki/Seiren