Marulk, a young Blue Whistle delver, serves at the Seeker Camp on the Abyss’s second layer under the White Whistle Ozen. Hailing from Jisweku’s royalty, he was born a “child of the shadows”—a hereditary condition marked by crippling sunlight sensitivity and a lifespan capped at ten years. His early years required protective “Moon Outfit” garments to survive daylight exposure. Following an airship crash in the Abyss that killed his father, Ozen rescued him, and he chose to stay as her apprentice.

At the Seeker Camp, Marulk operates the telescope to track approaching delvers and lowers the gondola for their descent. Though youthful, he displays basic delving proficiency, briefly surviving alone on the second layer. His short blue hair and maid-style outfit, selected by Ozen with functional additions like tool-storing head pockets, often lead others to misgender him, though he uses masculine pronouns.

Shy and polite, Marulk yearns for companionship amid his isolated duties. He harbors a blend of reverence and fear toward Ozen, yet trusts her guidance. When Riko and Reg arrive, he forms a heartfelt bond with them, voicing concern during Ozen’s harsh trials. Defying her orders to aid Reg in their clash reveals his growing resolve and empathy.

The spin-off *Marulk’s Daily Life* delves into his routines: maintaining the camp, aiding delvers, and rare surface visits to Orth, where he enlists Nat’s help navigating shops. In *Binary Star Falling into Darkness*, he acts as a quest-giver, showcasing his willingness to risk Ozen’s disapproval to assist others.

His royal “child of the shadows” lineage and adaptation to the Abyss underscore resilience and self-discovery. Across narratives, he navigates loyalty to Ozen and budding independence, embodying a caretaker’s compassion while confronting the Abyss’s unforgiving depths.