Wataru Ikusabe begins as an ordinary elementary student defined by athleticism and an unwavering moral compass. His life transforms when a mystical dragon whisks him to Soukaizan, a pyramid-shaped realm where he is declared the prophesied savior. To restore the world’s fractured rainbow, he must conquer each tiered level, merging his handmade clay robot with the dragon’s essence to forge the mecha Ryujinmaru—a pivotal weapon against demonic adversaries.

Later trials strip him of his innate compassion: a demon steals his "kind heart," erasing his heroic identity and plunging him into delinquency. Reentering the magical realm reignites his memories, compelling him to reclaim his stolen conscience by opposing the Donarukami clan—antagonists embodying societal erosion of empathy. This struggle intertwines his quest for redemption with broader themes of ethical decay.

A subsequent OVA chronicles his evolution as a fifth grader confronting apocalyptic threats from the demon world. Deprived of Ryujinmaru, he embarks alone to recover the Fist Dragon Magatama, trading mecha battles for a perilous, solitary odyssey. His mission pivots on mortal sacrifice, demanding he permanently seal encroaching evils through sheer resolve.

Allies shape his journey: the kunoichi Himiko, samurai Shibaraku, and newcomers Suzume and Seiju reinforce his reliance on camaraderie. His combat growth manifests in mastering techniques like Ryujinmaru’s dimension-cutting slash, symbolizing escalating prowess.

Rooted in themes of innocence and external influence, Wataru’s narrative frames heroism as a balance between action and introspection. His adventures blend whimsy with existential weight, interrogating how purpose and responsibility intertwine amid shifting moral landscapes.