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

Akari Miyamae suddenly barged into Motomu Shiraki's apartment. She was a good girl who loved her brother and rumors of her beauty extended even beyond her school. "I'll gladly become my senpai's property until my brother pays back his debt of 500 yen!" she declared happily. Motomu is bewildered by this outlandish turn of events, but Akari forcefully convinced him as she prepared to take up residence. Naturally, there's more to the story. The exciting life of living with a beautiful girl in a one-room apartment begins!

(Source: Kadokawa, translated)