This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Violinist of Hameln
Lute's backstory in the (manga).
Hamel's childhood before the disaster of Anthem. Living in abject poverty? Check. Loving mother whose sanity is slowly unraveling? Check. Being pelted with stones by children and adults alike? Check. Having your hometown invaded and being blamed for it? Check. Your mother frozen and carried away in front of your very eyes? Check. Snapping and killing everyone on sight except for the one friend you ever made, who promptly called you a monster and shunned you? Check. And he was so sweet and adorable. Humans Are Bastards.