Yuujin ni 500 Yen Kashitara Shakkin

“Until my brother returns the 500 yen, I will gladly become senpai’s property as collateral!“
One summer day, Akari Miyamae, his friend’s younger sister, came to the apartment of Motomu Shiragi, a university student. What is the secret behind this debt, and what is Akari’s purpose…?