Toshiya Dan is an 18-year-old second-generation pioneer born and raised on Jupiter's moon Io. His status as an Io native positions him directly in the conflict when future invaders, the Eldar, arrive from 250 years ahead and occupy the colony, threatening Earth. Toshiya serves as the main pilot of the combined super robot God Sigma, specifically operating the Sky Thunder King component unit. He spearheads the combination sequence into God Sigma alongside co-pilots Julie Noguchi and Kensaku Kira to counter Eldar assaults. His personal stake in liberating his occupied home drives his evolution from colonist to a pivotal Earth defender. Leading battles against Eldar commanders and their Cosmosaurus forces, Toshiya focuses on protecting Trinity City and its vital energy source. He survives the climactic mutual destruction of God Sigma and the Eldar mecha Gargos. Following the war, God Sigma is repaired and modified for single-pilot operation, allowing Toshiya to embark on a solo journey with the reconfigured machine.