This deserves a TW and mods feel free to flag it if it ruins any guidelines. I will block (blur it) incase.
For my old story, back from when I was 14 - 16, I had quite a long novel. At the end, the good guys win and all. There was the mentor of the story who at first was bad but was actually good all along. Super gruff guy who took no nonsense.
We end up learning that he is the brother of the antagonist, but his position as a mentor is more of a ploy to lead the MC to her death. Anyways, his backstory is kind of tragic.
TW for this part entirely:
TW please don't read if you struggle with mental health issues and may feel that this is a difficult topic for you.
We learn that he had a wife and young daughter that he loved dearly. However, his brother had both of them murdered, forcing the mentor into the program to catch the MC. This dude was broken hearted, he was a completely amazing dad and lost it like that.
Yet that's not the end of the sad part. It's the second to last chapter, after the big event happens and things boil down, that the MC receives a letter from this person. She hadn't heard from him in a few days. It reveals that this was his final letter and that he killed himself. He said that he wanted to be with his wife and daughter again. And now that he manages to help find his life purpose (saving the MC) he can't bear the pain of not having his family.
The MC is an utterly mess as she learns the same day that she is actually infertile. She was never interested in having kids right away, but it was sad to her.
So, yeah. That makes me cry everytime I think about the chapter.