my older sister is mine.

Rei, a young wife who married the boss of the company and lived with her brother-in-law. One day, she was told by her husband's guardian about the existence of a basement. He went to the basement with all his interest, but in fact it was the guard's nephew who tried to make her a comforter. As soon as he entered, his freedom was taken away from him and he was told that "Yoshie-san will live here from today," and since that day, the miserable life of being confined to the basement as a toy for his brother-in-law has opened.