Great Mazinger vs. Getter Robo G: Kuuchuu Dai-Gekitotsu

Fuente: AniList

When a UFO arrives from space and attacks the Getter Institute, Getter Robo is launched to stop it; but the might of the UFO and its giant space monsters prove to be too much for the Getter team. Not only is Getter Robo defeated, but Ouishan is killed in action! With Getter Robo out of commission, the world's only hope appears to be Great Mazinger, but the aliens' power might also be too much for even him. Can Dr. Saotome build a new Getter Robo in time to help save Great Mazinger, Japan, and the entire world?