The Kobayashi twins, Megumu and Mitsuru, were named after historical figures, but only Megumu has grown up with a taste for history. So when Mitsuru is in danger of losing his weekends to extra history classes, he convinces his sister to swap clothes with him and ace his tests After all, how hard can it be for them to play each other?

Megumu is almost done taking Mitsuru's make-up classes for him, and it's nearly time for the twins to go back to their own lives. But then catastrophe hits Megumu's true love, Aoi, discovers she's really a girl and goes into an allergic fit. How will she ever face him again? And even worse, Mitsuru's sworn enemy, Azusa, finds out he's really a dude. What will happen when she spills the secret to his sweetheart, Shino?