Dehdeh presents as an elderly woman, small in stature with a deeply lined face and distinctive buckteeth that define her unique appearance. Her past is rooted in the sea; an encounter with a boy from the ocean during her youth anchors her insight into its phenomena. She serves as guardian and watcher for Umi and Sora, boys of supernatural marine origin, vigilantly overseeing their well-being.

She further acts as a guide for protagonist Ruka Azumi, especially during unexplained marine and cosmic events. Dehdeh provides exposition on nature's interconnectedness, weaving explanations like the universe reflected in one's palm to illustrate humanity's bond with the cosmos. This philosophical guidance makes her a conduit for themes exploring humanity's place within natural systems. Her dialogue delves into metaphysical concepts, emphasizing parallels between microcosmic and macrocosmic patterns in nature, reinforcing the narrative's focus on universal bonds.

Dehdeh's involvement peaks during key transitions where marine anomalies escalate into cosmic manifestations. Her explanations to Ruka frame these events within broader existential contexts, not scientific rationale. Her narrative role remains consistent, facilitating protagonist development and reinforcing themes through her established perspective as both witness and interpreter of the sea's mysteries.