He and Lucia arrived on Earth with the purpose of exterminating humanity. He soon took an interest in the Gransazers, despite believing them to be too weak to fight him one-on-one. He later sent several Gig Fighters to attack a JSDF base to draw out the Gransazers so he could observe their power. After watching Tarious defeat the Gig Fighters with the Falcon Blow, Radia left the scene.
Tenma later came across several more Gig Fighters and transformed into Tarious to fight them. Radia then appears and ambushes Tarious and Gorbion. He introduces himself and vows to crush all the Gransazers. However, the two Gransazers force him to retreat, prompting him to swear a vendetta on them.
Later, when Lucia is wounded, Radia resolves to complete their mission on his own. He battled Gorbion and Pisces, transforming into a giant after his first defeat. However, Gans arrived and the Water Tribe were able to awaken Leviathan. Despite this, Radia refused to retreat from the fight and ended up being killed by Leviathan.