Kyun to Shite, Yamagami-kun!

Taiga and Yamagami were childhood friends, close like brothers...or were they? Their relationship became strained after Yamagami, who used to be a bit of a dodder, transformed into a high-spec, elite, glasses-wearing guy. "Oh, I wish I had a kinder, cuter female childhood friend." Whether Taiga's wish was granted or it was a whim of the gods, Yamagami was cursed with the following: "When he sneezes, he turns into a woman" and "When he feels love, he turns back into a man." (Taiga is cursed to remain a virgin forever.) The key to this "love" lies with his awful childhood friend, Taiga...!? (Source: Kadokawa, translated)