When sixth-grader Kei Nimori discovers his name mysteriously written on the blackboard with an enigmatic title, his ordinary life takes a fantastical turn. As the clock strikes midnight, a portal materializes in his room, transporting him to his school in an alternate dimension known as the 'Houkago.' In this eerie realm shrouded in darkness, classrooms are infested with strange entities called 'anonymous wonders.' Alongside five other students, Kei is tasked with documenting and studying these otherworldly creatures. Leveraging his artistic talent, Kei embarks on a mission to illustrate 'Makkaka-san,' a menacing monster haunting the rooftop of the school.