The man is an agent for the ministry of research. No one knows his name, only his code name, "September." His main duties are spying overseas, but on return from an assignment, he is suddenly ordered to spy on students at an all-girls' school, "Akisui." He's not too happy about the situation, but orders are orders...

Disguised as "Shun Mishima," he becomes a teacher, where he runs into an ex-girlfriend who once betrayed him, "Miyuki Jinnai." She hands him a drug, and even though he's been burned by her before, he gulps it down... He changes into a "girl!!" She tells him, "You now have a free pass around the school..."
Why did the ministry send him to this all-girls' school anyway? With the ability to switch identities, will he be able to clear up the mystery at the school?

[From Gamelex]