Houkagogakari

A sixth grader named Kei Nimori discovers his name written on a blackboard with a strange title. At midnight, he hears school bells and a portal appears, revealing his school in a dark alternate dimension known as Houkago. This version of the school is inhabited by creatures called "anonymous wonders." Kei and five others are brought to Houkago to observe and document the monsters they are assigned. Kei, skilled in drawing, uses a brush to sketch Makkaka-san, a creature hiding on the rooftop.