
I'm like.... 90% sure these characters are 3d models (or traced 3d models). I can't... I can't handle it. The mouths... I really want to read it. Is it based off a light novel?

As an artist myself I can 100% confirm that the artist here is posing 3D models and tracing over them.
I used to try out the 3D models that are included in Clip Studio Paint in the past back when I heavily struggled with anatomy but quickly gave up on them bc they made my art look pretty much exactly how the artwork on this mahnwa looks like.
I'd rather have fucked up anatomy that improves over time than the creepy uncanny vibes anatomy the 3D models create lol
I like how the MC is actually happy at the aspect of the sister leaving. I get how hard it can be to tell someone, especially your sister, when you're upset at them for something they do. Especially if it's something you're used to them doing. And she does get properly mad at her. Her sister is just too about herself to listen.