Sōsuke, a five-year-old boy born May 25, 2003, lives with his mother Lisa in a cliffside house overlooking the sea. Lisa works at a nearby retirement home. His father, ship captain Kōichi, is frequently absent due to work, influencing Sōsuke's daily life and responsibilities, especially when Lisa temporarily leaves him in charge. He possesses dark eyes, tan skin, and dark brown or black hair cut in a bowl style, showing noticeable grey roots. Sōsuke typically wears a short-sleeved yellow shirt and dark grey shorts, often barefoot or in uwabaki slippers. Reflecting his maritime interest, likely inspired by his father, he sometimes wears a sailor hat and uses binoculars. Intelligent, loyal, protective, and adaptable, Sōsuke discovers a goldfish trapped in a glass jar while exploring the seaside cove. He rescues her by breaking the jar with a rock, sustaining a minor cut on his thumb. The goldfish licks his wound, healing it instantly. Sōsuke names her Ponyo, promises protection, and takes her home in a green pail. He responsibly cares for her, offering food and attempting introductions to friends and retirement home residents. When a peer, Kumiko, insults Ponyo, Sōsuke defensively hides her away. His deep affection and commitment to Ponyo form his narrative core. He reiterates his protective promise even after her magical transformation into a human girl triggers a catastrophic tsunami flooding his town. Separated from his mother during the flood, Sōsuke takes initiative. Alongside Ponyo, he journeys across the submerged landscape using a toy boat enlarged by her magic. He displays leadership and caretaking, pushing the boat when her magic falters and supporting her as she weakens, determined to find his mother despite encountering Ponyo's father, Fujimoto, who distrusts humans and urges Sōsuke to return Ponyo to the sea. Sōsuke shares a close, supportive bond with his mother Lisa, attempting to mediate during her frustration over his father's absence. He demonstrates respect and maturity toward the elderly residents at her workplace. His interactions with Fujimoto show initial caution and defiance as he resists demands to relinquish Ponyo, later gaining Fujimoto's reluctant trust by proving his genuine commitment. A critical test occurs deep beneath the ocean within the protected nursing home. Reunited with his mother and encountering Ponyo's mother, the sea goddess Granmamare, Sōsuke is questioned whether he can accept and love Ponyo unconditionally regardless of her form. He confidently affirms his love for "all the Ponyos," demonstrating the sincerity and constancy fulfilling Granmamare's requirement. This acceptance allows Ponyo's permanent human transformation and restores nature's balance. Fujimoto ultimately respects his daughter's choice and Sōsuke's dedication. Sōsuke's background draws inspiration from Hayao Miyazaki's five-year-old son, Gorō Miyazaki. His name is written in hiragana as そうすけ (Sōsuke), carrying no inherent Japanese meaning. His physical appearance, particularly when wearing the sailor hat, occasionally draws comparison to Kanta from *My Neighbor Totoro*.