Maruruk is a Delver that lives in "Seeker Camp" of the 2nd layer of The Abyss alongside the legendary white whistle Ozen the Immovable. Despite his young age, he's already a Blue Whistle due to being a direct apprentice of a White Whistle.
At some point when he was very young, he fell down in an accident and nearly lost his life before being rescued by Ozen. Following the event, he chose to stay in the abyss and become Ozen's disciple but after some time his eyes developed an extreme sensitivity to the light, so he never returned to the surface. He's in charge of the telescope inside the camp, and is often keeping watch of the surroundings so that a gondola can be lowered when a delver shows up.
Maruruk is a young boy with short blue hair and a rounded face. His feminine traits and maid attire leads people mistakenly identified him as a girl, but he's actually a male. While the details are not clear, it's implied that Ozen was the one that forced him to dress like a maid.
He is a rather shy, but polite individual who missed having the chance to talk with people with the same age like him given the fact that he manages the Seeker Camp. Though he does fear Ozen at times, he knows her well and trusts her.
He's very reluctant to talk about his clothing. When Jiruo mentioned it, Maruruk became very nervous, despite greeting Jiruo as an old friend only moments before.
Maruruk has been trained in the basics of delving and displays enough skill and expertise to prove to be a blue whistle, despite his young age. As a direct apprentice of a white whistle, he's considerably more skilled at delving than kids his age, and he is capable of surviving on his own in less hazardous sections of the 2nd Layer for at least a couple of days.
- His name comes from "marulk," the Swedish word for "angler."