Be My Salvation (Ereri/Riren)

Orphaned at a young age, Eren's forced into the foster system, and after being shuffled around for several years, things in life finally seem to calm down. But life has never been kind, and the peace doesn't last long. After months of abuse and neglect, he's pushed back into a foster home where he'll meet a dark-haired musician who seemingly wants nothing to do with him.