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 manages to keep Aoi and Uesugi from brawling, but when they air their old grievances, she ends up learning more than she expected about Aoi's past. Will this new information strengthen her relationship with Aoi or just drive a bigger wedge between them?!