Everybody has a protection spirit. Their behavior has a direct influence on the person they protect. For instance, if protection spirit A falls in love with protection spirit B, then host of A will fall for the host of B (synchronized effect). Karin has Hiriji as a protection spirit and that's why he doesn't have friends. It all changes when Karin has a little incident and gets help from his sensei, Takatsugu, whose protection spirit is Nagi. Sensei is the school nurse and he can see, hear, and touch protection spirits and he was a playboy until he meet Karin (Hiriji).