Tonrariano the Third, known as Ton-chan or Iggy Pig, is a small yellow pig prince hailing from Buuringo—an apple-shaped planet also called Oinko—where he is heir to King Tonrariano the Second. His journey to Earth forms a critical trial for his royal ascension. Junior high student Karin Kokubu discovers him unconscious behind a bush; reviving him with an offered apple, she forges an instant bond that leads him to select her for a pivotal mission.

He gifts Karin a magical pink "Dream Compact," transforming her into the superheroine Tonde Buurin (Super Pig). This metamorphosis turns her into a pink piglet—a form she resents for its unconventional appearance. To incentivize her, he strikes a bargain: every good deed she performs as Buurin yields a pearl from a green shell. Accumulating 108 pearls through heroic acts will grant her any desired form. Serving as her advisor, he rigorously enforces the rules, cautioning against power misuse and pearl loss.

Beneath his carefree, bookish exterior, he harbors sincere worry and occasional remorse over Karin's struggles with her piglet identity. His fierce loyalty drives him to extreme measures to protect her secret, including impersonating Buurin when Karin must appear alongside her superhero self to avoid exposure. He imposes one irreversible law: if her dual identity is revealed, she remains a pig permanently.

He wields flight like Buurin, deploying it to assist her on missions while dwelling in Karin's room. Immersed in her daily life, he balances guiding her heroic growth with fulfilling his own royal trial through her triumphs. His narrative functions span mentorship, comedic interludes via antics, and upholding the magical system steering Karin’s quest.