The first thing you do when you become a girl: Waking up one morning, Natsuki realizes that he has turned into a girl. The situation is, to put it mildly, ambiguous. But no matter what happens, do not be discouraged - it is better to look at everything in a positive light. So he did, finding useful use for his new body.
The first thing you do when you become a girl 2 - Lesbian: Natsuki always liked Aya, except that Aya herself is afraid of guys. But a new body opens up so many possibilities, so why not mend a relationship?
The first thing you do when you become a girl 3 - School: It was just perfect. Damn Kaworu! Now Natsuki is just a toy in his hands.
The first thing you do when you become a girl - Subway Girl: A small offshoot from the main series. It happens, most likely, between the 3rd and 4th parts, when Natsuki, returning home, was lucky to come across an unusual train.
The first thing you do when you become a girl 4 - Final: The finale of the story will tell you what fate has in store for Natsuki. Will he be able to become a boy again or will he be a girl forever?