This Savage Song and Our Dark Duet is a middle grade duology, known as Monsters of Verity. My daughter and I affectionately refer to them as the August Needs a Hug books.
This is a universe where monsters are created when people commit horrific acts. August is one of those monsters, created from a school shooting. Kate is human, the daughter of a mobster who keeps people safe from the monsters by controlling them much like he controlled (controls? it’s not quite clear how in the past it is) his crime empire. Kate is on her way to becoming a different, very human kind of monster, while August just wants to be human.
These books are a very sweet story about two people who become friends and grow up under what can only be called very trying circumstances. Recommended if you’re at all into YA or that particular branch of science fiction.