This is based on opinion. Please don't list it on a work's trope example list.
Tearjerker / Before I Fall
Sam dying after she saves Juliet. To call it a Bittersweet Ending is putting it mildly. You realize everything Sam loses: her family, her friends, her future, marriage, college, kids, and everything she had to do or say with her life are gone. After spending 400 some odd pages with her. To say nothing of what her Love Interest, family, and best friends are implied to deal with grief wise.
While not the most dwelt on example give it's in the middle of another argument but when Sam accidentally insults Elody in the mids of calling out Lindsey it is very easy to feel sorry for Elody who while loved by her friends is implied to have a very bad home life with her parents alcoholism and Sam's revealing that Lindsey has made fun of her behind her back on it really hurts.