The UFO (UFOってなんでござるかの巻) is episode 16 of the 1981 Ninja Hattori-kun anime.
Kenichi finds a UFO in the sky - or does he?...
Kenichi has taken the job as a photographer for the school magazine and is hoping to find something interesting. Meanwhile, Kemumaki, who has been spying on the photographer, throws his shuriken. Kenichi apparently spots a UFO near the temple. He manages to get a photograph of it, tells Hattori, and gets the school talking. He then tries to take the gang to the temple to get a look, but only manages to get Shinzo, Shishimaru, Yumeko, Kemumaki and Koike because Hattori is unable to come due to training.
As soon as they get to the temple, the gang then sit down to eat and wait for the UFO to arrive. Kemumaki then runs off to a nearby forest and engages in a fierce duel with Hattori, who sends his shuriken flying. Kenichi, assuming it was the UFO, takes a photo of it.
The next day, however, Hattori tells Kenichi the truth that the so - called UFO was his shuriken both yesterday and the day before that. Kenichi is extremely crestfallen.