Spaak fled his home planet's destruction by Slash as a child, escaping aboard the Needle Tower with his sister, the Princess, to the Twelve Worlds. There, he rose to become the Great Child of Primas, acknowledged as the most powerful Great Child across all twelve realms. Renowned for heroic deeds like saving the Third World from a Giant Taurus and inspiring Kai to become its Great Child, or freeing Pinky from a family curse and motivating her own role, he gained admirers throughout the worlds. His combat prowess centered on twin swords for close-quarters fighting.

Witnessing Bucky's courage against a Trouble Monster in Primas, Spaak passed his title of Great Child to the boy, assuming the mantle of Great Soldier instead. He intermittently aided Bucky's subsequent journey across the worlds, notably reappearing to save Pinky from Slash. During the climax, Slash possessed Spaak's sister upon her awakening from cryostasis. To free her, Spaak employed the rare "Prayer of Heaven" ability, transferring Slash's possession from his sister to himself. As Slash took hold of him, Spaak urged Bucky to defeat Slash completely.

Following Slash's defeat, Spaak and his sister departed the Twelve Worlds on the Needle Tower to return home. The "Prayer of Heaven" was used only twice: first to redirect a curse away from Pinky, and second for his sacrificial act to save his sister. This unique ability, combined with his twin swordsmanship, defined his combat role.