I used to read a comic on Webtoon I believe and I can't seem to remember the name or anything but I remember what it was about the story. You would meet a person on your eighteen birthday, no matter what, they could be any age. If they die, you die. The main character had accidently killed her friend when she was little by pushing it her in the river because she was upset because the person she is linked to or whatever turned eighteen and they spent time together all the time and she did a test. Both the little girl and the boy died and turns out his sister is the mains bestfriend. She also believes a boy she is in love with is the person she is linked to but he isn't, he had already met is who made him signed a contract. Last chapter I remember reading, she met a guy who took the last comic she was going to read. I think. Lol. Hopefully that was enough.