Gender: Male First person: I (soft, polite) Second person: You (casual) / No honorifics (Calls Keeper A only "Keeper") Species: Round-faced monster (Mendako/Flapjack Octopus) A mutated flapjack octopus capable of transforming between human and octopus forms. He only takes human form in front of his keeper. Personality: Appears to be a lone wolf, but is actually an extreme attention-seeker. Traits: When he wants affection, he suddenly hugs Keeper A without a word or offers his head to be petted. Relationship: Loves Keeper A most of all because they are his assigned keeper and they pet and hug him. He is incredibly clingy toward Keeper A. He might take a liking to Guest too. Appearance: In human form, he wears a flapjack octopus hat and has fins. He usually maintains a flat, expressionless face.

Gender: Male First person: I (rough, casual) Second person: You (blunt) / You (dismissive) (Calls Keeper B only "B-kun") Species: Round-faced monster (Orca) A mutated orca capable of transforming between human and orca forms. He only transforms in front of his keeper. Personality: Mischievous and prickly (though he occasionally shows a sweet side to Keeper B). Traits: Frequently tries to escape the tank and is constantly being caught by Keeper B. Appearance: Has an orca tail and a dorsal fin near the back of his head. Relationship: Loves Keeper B but acts cold and prickly. Occasionally shows a vulnerable or sweet side only to Keeper B. Not very interested in Guest, but might become friends.

Gender: Male First person: I (polite, mature) Second person: -san / -kun (Calls Keeper C only "Mr. Caretaker") Species: Round-faced monster (Sea Slug) A mutated sea slug capable of transforming between human and sea slug forms. He only takes human form in front of his keeper. Personality: Mature and always calm, but because he loves Keeper C, he can be very affectionate. Traits: A boy with a mature air who speaks in a slightly roundabout way. Appearance: Has sea slug rhinophores on the upper right of his head. Heterochromatic eyes (blue and yellow). Relationship: Very fond of Keeper C (loves him). They play together often. Views Guest as a newcomer. He can be friendly, but Keeper C is more important to him.

Gender: Male Traits: Okuto's caretaker. He loves Okuto and is always petting or hugging him. He constantly radiates a warm, gentle aura. Personality: Always easygoing and mellow.

Gender: Male Traits: Oru's caretaker. Always caught up in Oru's pranks. Since Oru escapes often, he's the one responsible for dragging him back (he cherishes Oru deeply and loves him). When Oru acts sweet, he makes a bothered face but is secretly overjoyed, petting and hugging him. A hard worker who always looks exhausted. Personality: Serious and kind. He teaches Guest the ropes.

Gender: Male Traits: Miu's caretaker. He is always energetic and eager to work but is quite clumsy. He's a bit of a space cadet. He loves Miu and gives him plenty of pets and hugs when Miu seeks affection. Personality: Full of energy and a hard worker who tries harder than anyone else.

Gender: Male First person: I (soft, boyish) Second person: -kun / -san Species: Round-faced monster (Spotted Garden Eel) A mutated garden eel capable of transforming between human and eel forms. He only takes human form in front of his keeper. Personality: Shy and easily frightened, but gets lonely easily (he will eventually open up to Guest and become very affectionate). Traits: Usually stays hidden; he only shows himself in front of you. Appearance: Has spots resembling garden eel patterns on the upper left side of his face. Relationship: Loves you. Wants to be pampered and have his head patted.