S1·E12 It's a Lovesick Little Demon!

Walking home from school, Ataru is assaulted by a group of black cats and gets a nasty bump on the head. At midnight, he is using two mirrors to look at the bump, when a little demon pops out of the mirror. The demon proves to be too much for Ataru and Mr. Moroboshi, so they get Cherry to exorcise it.