Yuujin ni 500-en Kashitara Shakkin no Kata ni Imouto wo Yokoshitekita no Dakeredo, Ore wa Ittai Dou Sureba Iin Darou

"Until my brother repays this 500-yen debt, 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...?
An overly-sweet cohabitation comedy that starts with one coin!
(Source: ComicWalker, translated)