The character known as "Young Sphinx" in the 1983 film appears as a youthful offspring of a sphinx, characterized by a yellow-orange body and vibrant green mane. Referred to as Marusu in the Japanese release, the character remains unnamed in the English adaptation. Residing in a desert habitat, Marusu discovers the collapsed protagonists during their journey and later joins their quest after informing them of their mother’s absence. Though initially blunt—even using taunts like "bonehead"—Marusu balances this with perceptive empathy, such as reinterpreting a companion’s abandonment as a protective sacrifice.

A 2000 ecological short film features a separate sphinx aiding protagonists by summoning a time-travel entity, unrelated to Marusu’s storyline. The 2024 graphic novel reboot reimagines the sphinx mythology, introducing Marusu as the abducted daughter of a guardian sphinx tied to ancient Egyptian lore. This iteration reveals her lineage’s symbolic third eye, representing healing and wisdom, and positions her abduction as the inciting incident for the protagonists’ mission.

Design and narrative elements partially draw from a manga chapter featuring Piro, a timid male sphinx cub orphaned after his mother’s clash with Oedipus. While Marusu shares Piro’s visual traits, their personalities differ sharply: Marusu acts with assertive agency, directly engaging in conflict resolution rather than retreating into passivity.