I don't remember the name of this novel...:

It's a novel about some1 playing a video game in a classroom, the alarm goes off... he's too lazy to follow every1 out of the building and continu to play on his game device. 15 min later, he realize that there's blood everywhere outside and a girl trembling in the classroom. 2 min later the girl get eaten by a zombie... he run to get weapons in the "history" classroom I think. Then make his base upstairs, in the same building. lvl up after killing a few things (like game element). kill a few oni (demons I think). Finally he can pick a class (like warrior, mage, etc)...and choose some weird shit allowing him to control anything in the "room" he consider his living space, but with super weak stats.

the class is like "shut in" (some1 that stays too much in his room) and the term they used was like something around "homikari" or w/e... (can't remember the exact term)

Try looking under the "Zombie" tag?

https://www.mangaupdates.com/series.html?category=Zombie% 2Fs