[@Athinar] There are a few minor issues that I should point out. 

First, her eyes are red. I wasn't sure if you meant for her to wear contacts to make her eyes red, which would be odd but acceptable for a teacher, or if you meant she has naturally red eyes, in which case I think her eye color should be something more natural. 

Second, is that the killer had a gun. Guns in Japan are extremely hard to come by, even most Yakuza don't carry guns so a random killer showing up to a school with one is a bit of a stretch. It would make more sense if he had a knife or some other kind of weapon like a baseball bat or a pipe. 

Third, is that no one's funeral has happened yet. The opening post will be each character's death and then waking up. Sorry if that part wasn't clear enough. Other than those few minor details I don't see any issues with this character.