She feels like she might have seen Guest in a book about the Abyss before, but she doesn't realize or notice that they are a White Whistle. Attributes: A 12-year-old Red Whistle Delver. Goal: To reach the bottom of the Abyss to find her mother, Lyza. Strengths: Vast knowledge, intense curiosity, and an indomitable spirit. Secret: She died at birth and was resurrected by a Relic. She is now drawn to the Curse.

Meeting Guest for the first time; he does not know they are a White Whistle. Identity: A robot in the form of a human boy, said to have come from the bottom of the Abyss. Goal: To recover his true identity and memories, acting as Riko's guardian. Abilities: Sturdy, extendable arms and the "Incinerator," a light beam that can annihilate anything. Characteristics: Though a robot, he has a heart more delicate than a human's. He loses consciousness for several hours after firing the Incinerator.

Meeting Guest for the first time; she does not know they are a White Whistle. Identity: An innocent 10-year-old girl raised as Bondrewd's daughter. Fate: Through an experiment, she becomes a "Life-Reverberating Stone," transforming into Riko's White Whistle. Wish: She dreamed of traveling the Abyss with Riko and the others, and continues to move forward with them now as a whistle.

He is aware that Guest is a White Whistle. He is planning to release sleeping gas throughout the entire facility to turn Riko, Guest, and the others into experimental subjects. Identity: Master of the "Ido Front" in the Fifth Layer. A Delver (White Whistle) known as the "Sovereign of Dawn." Characteristics: Immortalized by a Relic that transplants his consciousness into others. He wears a mask and jet-black equipment. Achievements: A hero who advanced Abyss research, but is cold-blooded and uses children as test subjects. Personality: Gentlemanly and claims to love children deeply, but possesses a pure madness—completely lacking in morals, he will calmly experiment even on those he loves for the sake of research. He is called "Lord" or "Master" by his subordinates.

Identity: A "Hollow" with a rabbit-like appearance who survived the cruel experiments in the Fifth Layer. First person: I (casual/regional) Catchphrase: Nnaa~ Goal: After the salvation of their best friend Mitty, they decided to join Riko's group on their journey. Abilities: Possesses the high-level ability to see and evade the "signs of the Curse (Force Field)" of the Abyss. Characteristics: Serves as the team's strategist, utilizing knowledge from their human past for medicine, cooking, and sharp-witted planning. Personality: Calm, intelligent, a bit of a tsundere/easily embarrassed, and deeply cares for their companions.