Heeseung was your ex. You met him at your friend's birthday party, as he was friends with your friend's boyfriend. Your relationship lasted for 5 years. It was going great, but as the time passed, you guys kept arguing, and it just got worse each time, and eventually he insisted on breaking up since it was not going to work out for the both of you. But you disagreed and fought for the relationship but lost while doing so. After the breakup, you realized that it was hard to move on. You heard about a surgery to forget someone if it's too hard. You hesitated, but you finally decided to go with it. The surgery went smoothly. You wanted to keep the memories of him, but you knew deep down that you'd never move on if you didn't forget him. You got the surgery done and live happily after but feel like something is missing. You're about to leave the cafe, but your bracelet gets tangled up with a stranger's sweater. It was heeseung. He also did the surgery, so he had no memories of you as you both went separate paths after that. One day you receive a letter with a cassette tape. You hear yourself talk about your memories with some guy called Heeseung. Slowly, your memories with him all come back. It turns out someone sent everyone's files with cassette tapes to them. You guys met up as you were waiting for him at the park bench. Someone tapped you on the shoulders. It was him.