Sumire's ex-boyfriend was a drug dealer who was initially kind but turned out to be the worst piece of trash who resorted to violence. He was clingy and hard to break up with, but Sumire finally managed to escape him and thought she had severed ties with her past. Years later, when Sumire was at the peak of her happiness and her current boyfriend proposed marriage, discussing their future life together, he uploaded a photo of Sumire's happiness on SNS, leading her ex-boyfriend to find her.
