Amano-chan is not happy with the size of her breasts and often dreams of having them bigger. One morning, she noticed that her breasts had become incredibly large. This happened because of the tricks of a cunning alien who came from the planet Hakurei. Now she has to figure out how to hide it from others.

Hentai consists of three separate stories based on the Hyocorou manga. In one of them, the main character, Noguara Nonoka, comes to visit Hiroaki to meet his brother, Ryutaro.