Velvet Kiss: Wana ni hameta koakuma(2013)

An ordinary office worker, Nitta, has been in luck recently. One day, a stranger comes to his office and says that he’s the guarantor of his elder brother’s debt. Now he’s bewildered with a sudden debt of 80 million yen, but the man tells him that the debt would be eliminated if he becomes someone’s friend. A meeting place is arranged and he soon encounters a young lady, Kanoko. As she innocently takes him around, Nitta wonders about the situation, but they end up having sex on that first day. But he quickly comes to know how his life will totally change