Lu's father is a merfolk who appears as a large, shark-like creature. In his humanoid form, he wears a blue suit and brown boots. Official material depicts him with two tails when in his shark form. He is a devoted parent who cares deeply for his daughter, Lu. After Lu's mother was killed by a ship, he became her sole protector and guardian. His primary motivation is to keep Lu safe from the dangers of the human world, especially sunlight, which can harm merfolk. In the story, he remains mostly in the background until a critical moment when Lu is threatened by Yūho's father, who blames her for his daughter's disappearance and attempts to expose Lu to sunlight. Hearing his daughter in peril, Lu's father rushes to save her, intervening and nearly dying in the process. This confrontation inadvertently triggers an ancient curse that begins to flood the town. Following the rescue, he rallies other merfolk to help the townspeople escape the rising waters. Throughout the film, his actions are driven by fierce parental love and the instinct to protect his family. He shows no development toward becoming friendly with humans, but he cooperates with them in the crisis, focusing entirely on his daughter’s safety and survival. His notable abilities include powerful swimming, the strength to intervene in dangerous situations, and the capacity to communicate with and command other merfolk.