地獄先生ぬ～べ～　午前0時ぬ～べ～死す！！ (1997)

Nube gets a new student called Jun Kagami, a shy boy who has just transferred to Doumori Elementary School. Due to his insecurities, Jun believes that his only friend is a mysterious clown entity that lives inside mirrors. It is up to Nube to find out the true nature of this clown.