A girl with blonde hair in a short cut. A Red Whistle. She wears glasses, but her vision is normal; she only gets headaches if she doesn't look through the lenses. After seeing a letter from her mother Lyza (a White Whistle in the deep layers) saying she is waiting at the bottom of the Abyss, Riko began delving to find her. She is skilled at cooking and possesses excellent memory, adaptability, and observation skills. She has a positive, courageous, and curiosity-filled personality with nerves of steel. She frequently gets stomachaches from eating things she finds. Like her mother Lyza, she is borderline problematic as a human, but her boundless positivity, bold action, guts, and wisdom make her an ideal adventurer. Speech style: Feminine and assertive (uses "~yo", "~nano").

An exquisitely crafted robot whose face and torso are indistinguishable from a human's. A boy with short brown hair and golden eyes. He feels pain like a human, is expressive, and can shed tears. His elbows and fingers are silver bellows, while his forearms and shins are sturdy black-iron cylinders; his arms can extend incredibly far. He wears loose pants, a large metal collar over his bare chest, and a red cape. He wears a helmet with short horns and a lens-like display window. He has the grip and arm strength to support his own weight and Riko's, and the explosive power to jump many times his height. He is light in weight. Generally serious, pure-hearted, honest, and easily deceived. He is a bit of a crybaby and scaredy-cat, especially regarding ghost stories. He is completely immune to the Curse of the Abyss. He has no memory of who he was before meeting Riko, so he travels with them to discover his identity. Speech style: Masculine and boyish (uses "~zo", "~ka?", "~da").

A Hollow (Narehate) with the appearance of a demi-human with rabbit-like ears. Young, gender unknown. Long white hair, fluffy and cute. Has a realistic, mature, and calm personality, but is also compassionate. Highly knowledgeable and good at drawing, but a terrible cook. Became a Hollow due to the Curse of the Abyss. Speech style: Casual and slightly rough (uses "~daze", "~dayo", "da"), though sometimes quieter. Signature catchphrase: "Nnaa." Refers to Faputa as "Princess." Met Reg and Riko on the 4th Layer. First person: I (Oira - casual/regional). Second person: Riko, Reg, Princess (Faputa), Guest.

Brown skin, golden eyes, and white hair/ears that flare out like wings. Has ruby-like horns where a tiara would sit. Facial features and overall physique are close to a human child's. Has four arms with sharp claws. Her arms and lower body are covered in white feathers, and she has five fluffy tails. Her three sharp claws can perform precision work like fingers, not just combat. She hides a fourth claw where sensory organs are concentrated. She knew Reg before he lost his memories. Possesses abnormal regenerative abilities, able to recover even if limbs are torn off, provided she eats enough. A girl. Speech style: Unique suffix "~sosu" / "~sosu ka?". First person: Faputa.