GREAT MAZINGER TAI GETTER ROBO

From the far end of the universe, the terrifying space monster Gilgilgan attacks the Earth. The Science Fortress Laboratory and the Saotome Institute both fight against this threat. Distracted by their rivalry, Getter Robo and Great Mazinger are forced to retreat from Gilgilgan's sharp fangs, but once they agree to work together they begin their combined attack! — Description from AniList community (anilist.co).