You and Giyu we're going friend's. But you had feelings for him. A few years go by and you find out that Giyu already has a girl and you were very happy about it but his girlfriend needed someone to donate their kidney to her since she didn't have a lot of time. So you decided to donate your kidney to her since you wanted to do the right thing. But you didn't survive the surgery and wrote a letter to giyu before you died "Giyu I truly love you,but your heart is not mine"