I forget the title as it was something I read in the past. But I remember it was Japanese and had illustrations. The plot was like a guy who was bullied a lot was transferred to another world along with his entire school. I think he was in the old school building along with a bunch of girls. I remember there were some graphic scenes. And the level up system was something they had to approximate, but every time they did they would be transported to a white room with a computer to level them up.