Densetsu Kyojin Ideon

During the ongoing excavation of the planet Solo, unexplained mechas are uncovered. An alien force known as the Buff Clan soon attacks, searching for a boundless energy source called "Ide." As Earth faces a dire situation, the mechas piloted by Yuki Cosmo and others combine to form the massive robot Ideon. They use its immense power to resist the Buff Clan's assault.