Eugh same... But ig she's one of those goody two shoes (╬￣皿￣)
I think it's mainly because in the end she wasn't treated super badly. They put her aside but she was still looked after. Except for the Prince and his yes men no one else disliked her. They were extremely rude. But Sei mind got occupied by something else she was surrounded by people that love her so the anger boiled down.. Plus she was the older one so in her eyes the Prince was just a reckless brat. Not to mentioned Sei didn't care being the "saint" and didn't like the attention.
What I found most unforgivable is the attitude of Prince & nobles in general.
The first Prince made grave claims and jeopardize their collaboration with the real saint. Even after the real saint reveal the Prince continues to preach that Aira is a saint. He apologized but it was never genuine. Even the ML's brother mentioned that despite the misundertanding was cleared by the king there are still those that believe Aira is a saint. What anger me most is that the bratty Prince didn't learn a single thing. His apology wasn't genuine. It was done bc he didn't want Aira to get a bad rep thus he took the blame. He did not acknowledge Sei as saint like ever. Even now. His attitude is very "She's everyone saint but the only saint I believe is Aira." What he thought was good for Aira turned out bad made the girl more insecure, pressured by expectations, fearful of what other will say is she reveal that her status says "mage" and got all women isolate her. The best thing he did for Aira other than taking the blame is leaving her alone to be frank.
P.s. Read Aira's spinoff! It's good!
I don't like how sei forgave them so easily, like i know she's more mature than me and i know they apologized but come onnnnn.. it took them 7 months to apologize properly, in my opinion that would've been enough for me to be resolute in not forgiving them. It just feels like they're invalidating her feelings a bit too much, i hate it.