Rosario + Vampire, Volume 1 (Rosario + Vampire #1-4)

Tsukune Aono, an average student who is unable to enter a regular high school because he flunked the entrance exams, enrolls at Yokai Academy and discovers it is a school for monsters where he is the only human. He is about to give up until he meets Moka Akashiya, a beautiful vampire who immediately takes a liking to him and becomes his friend.

When other students threaten him and Moka, he finds that he can remove the rosary from Moka's necklace and have her transform into a powerful vampire. Rival classmate Kurumu Korono tries to attract Tsukune by charming him as a succubus, but Moka defeats her. When the clubs recruit members, Tsukune tries out the swim club, only to discover that its team members are deadly mermaids. He, Moka, and Kurumu join the Newspaper Club where they meet club president Ginei Morioka; a girl-chasing playboy who reveals to be a werewolf after he abducts Moka.