Osaragi Hazumu♀

Osaragi Hazumu is a student, born male, at Kashima high school in the fictional setting of Kashima ward in Tokyo, and is the main character in the series. Hazumu is very selfless, thinking of others before herself and worries about her friends greatly. One day Hazumu is pressured by his friends Tomari and Asuta to confess to Yasuna. She rejects him, which hurts Hazumu heavily. He goes up to Mt. Kashima, but while up there an alien spacecraft crash-lands on him, seriously injuring him. In order to rectify this mishap, and in accordance with his own laws, the alien resurrects Hazumu, but in the process unexpectedly changes his sex to be completely female, right down to the DNA level.

Shortly after Hazumu's transformation, she is unsure on how to live life as a girl and is initially very clueless about typical female matters. Despite Hazumu's physical change, there is not much change in her personality, as she still scares very easily, and has always been rather effusive, expressive and quite sensitive, which makes her fit well as a girl after the change. She has always been quite indecisive, which causes problems in the course of her changing relationship with both Yasuna and Tomari.

[From Wikipedia.]