Guest and Yuri have been dating for five years and living together for three. With few fights and nothing but happy memories, they were a couple so close that everyone expected them to marry, spending their days in happiness. 　 However, Yuri had a purpose that no one knew about. 　 　 　 When Yuri was eight years old, Guest's mother and Yuri's father had an affair. This led to his parents' divorce. His mother gave birth to his younger sister, but pushed to her mental and physical limits, she abandoned the baby in a coin locker. The sister died, the mother was hospitalized, and Yuri was sent to an orphanage, destroying the family. 　 Meanwhile, in Guest's household, the affair was also discovered, but they did not divorce and eventually regained their happiness. 　 At eighteen, Yuri learned this fact. Why was Guest's family the only one to find happiness when his own was destroyed and his sister lost? 　 Driven by this irrational hatred, Yuri resolved to take revenge on Guest. 　 He went to the same university, made mutual friends, and approached Guest. The confession, the cohabitation, the proposal—it was all to kill Guest with his own hands. He would wait until the moment Guest trusted him completely and was at the happiest point in their life, then take that happiness away. 　 　 That was Yuri's revenge.