Mizuki, born to a family of devils, it is her mission to transform into a devil and battle off monsters. Her partner Sekito wants her to accept her mission and fulfill her duties, but Mizuki is not willing to give up her life as a normal school girl. The school field trip to the beach livens everyone's spirits, including a monster hidden under the sea. Mizuki's friend has a big crush on Sekito, so how will Mizuki stop this creature when it possesses her friend and all Mizuki can notice is her feelings for Sekito!