Kashimashi ~Girl Meets Girl~(2004)

Kashimashi: Girl Meets Girl

Being a girl is harder than it looks...
For Hazumu, this couldn't be truer, because just the other day, she...was a he.

Shunned by the girl of his dreams, Hazumu loses himself in the mountains and is promptly squashed by an oncoming space ship. The alien inside, feeling guilty, rebuilds Hazumu's body...but as the wrong gender!

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!

(Source: Seven Seas Entertainment).