Haruka finds a cat in an abandoned building and names it "Nyan". Little does she know that this cat is actually "Ultra-Nyan" who has come from outer space. Using his mysterious powers, Ultra-Nyan helps Haruka and her friends foil the plans of a couple of no-good catnappers.

The film was double-billed with the tokusatsu film Ultraman Zearth 2: Choujin Taisen - Hika to Kage (Ultraman Zearth 2: Superman Big Battle - Light and Shadow).