Ikusabe Wataru is the main protagonist of his series, an ordinary Japanese elementary school student who is summoned to another world to become its chosen savior. He is a ten-year-old boy who attends Ryujin Elementary School and lives with both of his parents as part of a nuclear family. At the start of his journey, he is a fourth-grader with a birthday on May 5th. He is a child of average height and build, with characteristic bounce-prone black-brown hair and a distinctive nose that are considered his charming points. As the legendary savior, he dons a formal white and blue attire accented with red and white shoulder pads, a gold crown tiara, white shoes, and carries a broad sword in a red sheath.

Wataru is defined by a bright, cheerful, and happy-go-lucky personality. He is an energetic and ambitious boy who readily tackles any challenge without worrying about the odds against him, though this can sometimes lead to overconfidence. His defining trait is a powerful sense of justice, as he refuses to tolerate bullying, lies, or cheating and cannot turn his back on the helpless. In his everyday life, he behaves like a typical active boy, excelling in sports such as baseball, soccer, and roller skating. He holds aspirations of becoming a Little League pitcher and an astronaut. However, his academic performance is average at best, and he dislikes studying and has a strong aversion to certain vegetables, including onions, konjac, and carrots. He has a habit of rubbing his nose with the back of his fist and is known to become very uncomfortable and frightened in the presence of snakes.

Wataru is transported to the magical realm of Soukaizan after placing magatama beads he found at a local lake onto a clay model he made in art class. This act summons a yellow dragon, Ryujinmaru, who becomes his guardian partner. According to the people of Soukaizan, he is the reincarnation of a legendary savior who saved the world from great darkness thousands of years ago, a destiny tied to the bloodline of the Ikusabe clan. His primary mission is to liberate the seven layers of the holy mountain Soukaizan from an evil demonic ruler and restore the colors of its rainbow. Throughout this quest, he forms crucial alliances with a young ninja girl named Himiko Shinobibe and a skilled samurai warrior named Shibaraku Tsurugibe. He also develops a complex relationship with his rival, the prince of the demon world, Toraoh, which evolves from enmity to a deep friendship.

Throughout his adventures, Wataru demonstrates significant development as a hero. Although he initially jumps at the call to adventure, he later shows signs of self-doubt, admitting that he never saw himself as someone capable of saving the world and that his strong sense of duty is what keeps him going. At one point, his good heart is stolen by an antagonist, causing him to lose his heroic memories and become a delinquent, only to regain his identity upon reuniting with Ryujinmaru. On another occasion, when tricked into believing that a friend has been killed, he experiences uncontrollable rage. His growth is intertwined with his ability to pilot Ryujinmaru, which powers up as Wataru himself grows mentally. Notably, he shows great adaptability and cleverness, crossdressing on several occasions as a disguise to infiltrate enemy territory. His core identity remains that of a child who combines innocence with the heavy weight of a world-saving prophecy, driven by compassion and resilience against overwhelming cosmic threats.