Obaba is a mystical sea hag dwelling beneath the ocean. She possesses profound knowledge of transformation magic and assists the protagonist, Mako Urashima, by granting her wish to become human. This aid involves Obaba giving Mako a pearl potion that triggers a permanent metamorphosis from mermaid to human. The transformation process is intensely painful and dangerous. In the manga adaptation, this metamorphosis occurs underwater, while the anime portrays it happening on land.

Obaba also bestows upon Mako the magical pendant called the "Life of the Mermaid" or "Tear of the Mermaid." This artifact grants Mako abilities essential for navigating her new human life and remains a crucial symbol of her oceanic origins throughout her journey. Within the manga narrative, Obaba further supports Mako by gifting her a magic telescope to help a traumatized child character, reinforcing her role as a provider of mystical tools.

Her involvement is strictly limited to Mako's origin story. She facilitates the initial transformation, provides the pendant and telescope, and has no further narrative development or appearances beyond this. The character lacks detailed personal history, motivations, or evolution across official media, maintaining a static role solely as a catalyst for the protagonist's journey. Adaptational differences exist: the manga presents Obaba's magic and its consequences in a less graphic manner compared to the anime, aligning with its child-friendly tone.