hiii good question ahaha 🥺 I've only been rereading fics recently and the last fic I reread that made my heart ACHE would be 'this side of paradise' by vikkie (arkastadt) the angst hurts so good so you can read it if you haven't!! another I would say is 'thunder in your lungs' by Chu_Penguinn (I'll link it!), it's de-aged chuuya and he's basically reverted back to during the time he was in the lab so it's heartbreaking 🥺