Yuu lives with her older brother, just the two of them together.
Having lost their parents at an early age, the elder brother started working to support the two of them and they lived together peacefully, taking care of each other.
Yuu loves her older brother very much, and the two of them live in a cramped one room space. With no room to spare, they also sleep in the same bed together.

One day, Yuu made up her mind. "Onii-chan, please have sex with me."