“I have come as collateral for my brother’s debt. I will be in your care from now on.” Miyamae Akari suddenly barged into Shiragi Motomu’s apartment. She was a good girl who loved her brother and was rumored to be a beautiful girl throughout the grade. But suddenly she offered herself as collateral for her brother’s debt. And that too, for 500 yen. “I’ll gladly become senpai’s belonging until my brother pays back his debt!” She declared happily. Motomu is bewildered by this outlandish turn of events, but Akari forcefully convinces him and steadily prepares to take up residence. Naturally, there’s more to the story. The exciting life of living together with a beautiful girl in a one-room apartment begins!