I think its more like he's trapping students in a time limbo in its own memories, thats why Dokkaebi and Minchan went to the school in order to exorcise an evil spirit. I think the friend only reverses the time when he reaches the last of his memories/time alive.
It DID NOT FUCKING WORK OUT SATORU YOU FREAKING DIED NIGA
hey so this shit is crazy if you're not a black person