Gamera vs. Guiron (1969)

Two boys, Akio and Tom, spy in their telescope a spaceship that descends into a nearby field. With Akio's little sister in town, they ride out to the field on their bicycles the next day to investigate. The boys enter the spaceship and accidentally take off to an alien planet named Terra, while Tomoko is left behind, unable to convince any adults, except the kindly but eccentric police officer Kondo, of the boys' misadventure. On Terra, the boys encounter two beautiful but sinister Terran women and their 'guard dog,' Guiron, who kills a Space Gyaos attempting to attack. Later on, it is revealed that the two Terran women plan to eat Akio and Tom's brains for sustenance. Gamera, sensing danger, eventually tracks the boys to Terra and kills Guiron (with both Terrans dying after their base is destroyed by Guiron) after a long and difficult battle, Gamera, Akio, and Tom go back to Earth.