Aristurtle (Moelle in Japanese) is the eldest and wisest sea turtle in the ocean realm, serving as an advisor to the sea kingdom's royalty, especially Prince Sirius. After jellyfish attack during Sirius's absence, Aristurtle confronts the prince, urging him to abandon his forbidden relationship with Malta, the fire princess, citing the ancient laws dividing their peoples.

His perspective shifts when he witnesses Sirius enduring the heat near the Holy Flame and Malta emerging unharmed from the sea, events defying the belief that fire and water children cannot coexist. Recognizing the unique power of their bond, Aristurtle transitions from discouraging their relationship to actively supporting it. He reveals a crucial legend: during a solar eclipse, Klaesco blossoms (Kalea flowers in the English dub) bloom on Mobius Hill (Hill of Elysium in the dub). Their spores ascend to a distant star where fire and water exist harmoniously as they once did. He identifies this as their only potential path to a life together.

Later, when antagonist Mabuse (Mugwug) discovers Sirius and Malta's plan to reach Mobius Hill, Aristurtle attempts to intervene. He chases Mabuse to prevent him from revealing their secret, though this effort ultimately fails. His actions directly facilitate the lovers' quest by providing them with both hope and a specific destination, despite the tragic outcome.