Ruka, a white dolphin, serves as a pivotal guardian in the protagonist’s survival and quest. When the protagonist’s clan is destroyed, she rescues the orphaned child, ferrying him to hidden coastal caves in Japan to shield him from enemies targeting his bloodline. A steadfast ally, she accompanies him alongside fellow dolphins Uru, Karu, and Fin during his vengeful journey, aiding in tactical strikes against adversaries.

Ruka’s strategic prowess proves vital in battles against antagonistic forces, from infiltrating enemy strongholds to confronting entities endangering marine life. She orchestrates critical maneuvers, such as luring a monstrous progeny of the antagonist onto land to ensure its defeat.

Her protective instincts extend to the protagonist’s family after he marries and has children. She intervenes during human-induced crises, rescuing a captured child and thwarting hunters targeting the family.

In the final clash against the primary antagonist, Ruka stands beside the protagonist, helping secure victory. After his disappearance, her enduring legacy safeguards his descendants, who find refuge on a sanctuary guarded by a colossal turtle ally.