Yuuka's boyfriend/husband has a brother in the band "Zero Sum" as the lead singer. After a request, she and her husband Yazaki got tickets to go backstage at a concert. However afterwards, all the band members, except Keith the leader, kidnapped her and raped her on the roof top all as a scheme by Keith who is madly in love with his brother. Now she can't forget nor can she get away.

(Source: Anime News Network)