An intelligent alien that came to Earth wielding the superior technology of its homeworld, Planet Mefilas. Alien Mefilas possesses many psychic abilities and is also adept at physical combat, but since “conquering the Earth by force is against [its] principles”, it devises a plan to tempt the heart of a young boy to give him the Earth.

Hiding itself in Mt. Tatsugasawa, it used its anti-gravity beam to imprison SSSP members Hayata, Akiko, and Akiko’s younger brother Satoru in its flying saucer. He offered eternal life as the condition for a trade and tried to have Satoru reply “I’ll give you the Earth” but Satoru resolutely refused his offer. This prompted Mefilas to turn violent, turning Akiko giant and making her destroy buildings, and then made other enemies like Alien Baltan appear.

However, Captain Muramatsu and his team were able to locate Alien Mefilas’ saucer and get inside. Alien Meflias released Akiko and Satoru and then began to fight with Ultraman who arrived on the scene. It reflected all of Ultraman’s beam attacks and held its own in physical combat too, but realizing Satoru never once gave into temptation, it admitted its own defeat and stopped fighting. Finally, it left the Earth, vowing to return and test the hearts of Earthlings one more time.