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

友人に500円貸したら借金のカタに妹をよこしてきたのだけれど、俺は一体どうすればいいんだろう

"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.