An ordinary earth boy was transformed into a murder weapon in an accident. When he was 15 years old, an employer asked him to kill his parents. However, the protagonist remembered the past with his parents because of his 6-year-old sister. That year, his sister was just born. The boy wanted to go to his father and said that he was involved in an alien's plan to transform humans. However, because the experiment was broken, he wandered around the universe and became the number one killer in the universe. Because he has a pair of wings that are half black and half white, he is called a fallen angel... What will happen if he is turned into a girl by an alien queen a year later...