Plot of this game?

[CandyFuru]

So I watched other people play this game however I'm still confused about what happened especially at the end where she shoots the boy but found herself dead

[Beridok]

There are already topics about this.
https://steamcommunity.com/app/964350/discussions/0/1752358461527849482/
https://steamcommunity.com/app/964350/discussions/0/1736595227851606570/

Quick summary:
Girl was murdered by robber.
Robber watched house days before you know that from one of endings, where you can read diary
Dead girl made pact with evil and she relives the day in "Groundhog Day" manner.
She is trying to have a revenge against Redhead Boy.
If you put whole 3 weeks (playthroughs) into one - then you get the last, final reiteration of "story". For that you might need a secret...