Beasts Made of Night (2017)

Taj is the most talented of the aki, young sin-eaters indentured by the mages to slay the sin-beasts. But Taj's livelihood comes at a terrible cost. When he kills a sin-beast, a tattoo of the beast appears on his skin while the guilt of committing the sin appears on his mind. Most aki are driven mad by the process, but 17-year-old Taj is cocky and desperate to provide for his family.