At the start of Kashimashi, a young high school boy named Hazumu Osaragi declares his love to classmate and close friend Yasuna Kamiizumi, but she quickly rejects him. Dejected, Hazumu climbs Mt. Kashima and is killed when an alien spacecraft accidentally crash lands on him. To rectify this, the alien in the ship named Hitoshi Sora brings Hazumu back to life, but inadvertently regenerates him as a female right down to the DNA level. This change in Hazumu serves as the catalyst for the development of character interactions for the remainder of the series. Now Hazumu must learn how to be the girl his parents always wanted while dealing with the trials and tribulations of being caught in a love triangle between two girls–his childhood friend, Tomari, and Yasuna, the girl who rejected him but is now strangely attracted to him/her!