I watched this drama on TV about a man double-timing his girlfriend with a gay guy and then the girlfriend and the gay guy started fighting but then the boyfriend left them so the two became best friends and raised a child together???
So now all I can think of is Rin and Makoto having a common asshole boyfriend, and Rin finds out he’s cheating so he storms in to confront Makoto but he realizes that 1) Makoto doesn’t know, 2) Makoto might be the nicest person alive who feels guilty anyway even if he doesn’t know about the cheating, 3) his boyfriend is the actual worst for bringing pain into Makoto’s life.
So Rin and Makoto commiserate over their shared pain and ends up becoming friends, and possibly dates in the future. (Or they could be platonic too like the TV show and raise a child together who they will name Haruka, idk, I’m not choosy.)