Such Lovely Skin

When Vivian, a 17-year-old Twitch streamer, confesses to an "NPC" in a videogame that she killed her baby sister, she welcomes a demonic mimic into her life.

This mimic is so accurate it can fool anyone, even her parents. It has ruined countless lives before Vivian's--other streamers and people spanning back centuries. To stop it, or even just survive it, she will have to follow its chain of victims back and embark on a journey to meet its only remaining survivor before it destroys her life and the lives of everyone she loves.

Vivian's slashed her way through plenty of bad guys and boss battles online but killing a demon IRL is a bit harder--especially when the more misery the demon causes her, the stronger it becomes.