This live-action TV series is the first of many adaptations of the popular manga series by Moto Abiko, one half of the legendary gag manga duo known as Fujiko Fujio. The 1980s anime series was a monster hit in Japan, and the most recent (2013-2015) anime incarnation was quite successful as well.
Hattori-kun is a ninja of the Iga Ninpo School who has just completed his training, and is sent off to wander Japan honing his skills. He is befriended by Kenichi Mistuba, a suburban middle school boy, and ends up moving in with his family. This is definitely a fish out of water story. Hattori seems to have spent most of his life sheltered away in ninja training, and isn't at all familiar with cars, televisions, or other aspects of modern life.
Produced by Toei Television Productions and NET (later TV Asahi), this offbeat mix of ninja action and family sitcom is off the charts weird. In order to match the look of the main character's manga design, they've used a child actor (actually two identical twin child actors) wearing a mask, with an adult actor providing the voice.