how gojo felt knowing his ward, the inheritor of an extremely powerful clan technique, fell for his best friend, a kid who swallows curses, just like geto
analysis on kirei & rin i made a while ago:
kirei kotomine is a monster, but he was never rin’s zouken.
the fan theory that kirei abused rin prior to fsn completely flattens their dynamic. if he had, her response to his "death" via caster in ubw would’ve been relief, not genuine worry. the church money incident wasn't malicious, nasu confirmed kirei genuinely just sucked at managing the estate funds and thought poverty would be a good lesson for rin. in fact, urobuchi + nasu noted that if tokiomi had lived, rin would’ve been a lot more unhappier. kirei killing him accidentally gave her freedom.
kirei actually cared for her in the past. Ex: in the fate/zero drama cds, when young rin goes missing, tokiomi doesn't even notice, only her mom and kirei do, sending kirei out to find her. the fz manga/novels even show kirei fearing the idea of rin becoming like him and actually enjoying his time with her.
nasu drops the biggest hint of their dynamic in the saber route. kirei leaves rin in a pool of blood but chooses not to kill her. kirei also doesn't tell rin that he was the one who killed her dad. this blind spot gives rin the opportunity to give shirou the azoth dagger that kirei gifted her to kill him. shirou kills him with it, kirei muses that gifting it to "some girl" (rin) ten years ago was why he became "so weak." his sentimentality for rin was his literal downfall and it's a significant part to note because rin held no more use for kirei at this point. he already got what he wanted with illya.
in ubw, the one route where he commits to killing her, he deliberately tells her he killed her dad to break her spirit, marking the final end of their 10-year status quo. yet he still prolongs the killing, asking for her last words and praising her resilience. this exact hesitation gives lancer the opening to kill him. Imo, just like the saber route, treating rin differently than his usual targets was what caused his death. and in hf, he goes out of his way to heal her after sakura's attack when he absolutely didn't have to given sakura had already become dark sakura by this point (unless I missed something).
even fate/unlimited codes (written by nasu) doubles down on this. in kirei's arcade route, he only kills her because she refuses to back down after gil told her kirei killed her dad, telling her to "rest in peace." he never had any intention of killing her in his FUC story. his defeat line for her says: "it was thanks to you that i enjoyed the last ten years as much as i did, rin." in rin's ending, she thanks him because she wouldn't have survived without the skills he taught her: "Our... lives finally part here, kirei. You were a fine teacher, but a horrible priest."
when media like emiya gohan shows rin making him mapo tofu after kirei gives her presents, it’s not erasing trauma. it's faithful to canon because kirei never abused her.
in the saber route manga, there's a scene where rin says kirei had the eyes of a father when he looked at her child self in flashbacks.
the ultimate tragedy of the tohsaka sisters is that a literal soulless sadist managed to be a better guardian to rin than zouken was to sakura. they were both used for the grail, but kirei's twisted mentorship gave rin more than what zouken did for sakura.