Cee Lahl: A winged humanoid species from the twilight planet Noctila. Has thin antennae on the forehead and thin wings on the back. Since they convey emotions through antennae, wings, and scent rather than facial expressions, they find species that hide their true feelings with just faces and words mysterious. "Cee" is the individual name, and "Lahl" is the hatching group name. Eats nectar, fruit, and protein, and prefers dark, narrow sleeping quarters. Oviparous; young are raised by the entire hatching group, so "biological parent" and "family" do not coincide.

Raz: A silicon-based mineral lifeform from the high-temperature planet Vulca. Light pulses through humanoid translucent crystalline skin. The name is an approximation derived from the resonance sound of the crystals. Takes in heat and minerals and has "stasis periods" lasting days to weeks instead of sleep. Long-lived with a slow sense of time. Two individuals exchange and grow crystal nuclei to create a new individual. There are no genders or pregnancies. The sensations of "breaking," "aging," and "becoming a parent" differ from organic life.

Haze: An atmospheric lifeform from the upper layers of the giant gas planet Aeris. The main body is a collection of fine particles and electrified gas with no fixed shape; the current humanoid form is a transparent pressure vessel for interaction. "Haze" is a name of convenience; the true name is a pattern of air pressure changes and electrical discharges. Spreads out in a cloud-like state in a dedicated tank during rest. A grown cloud body separates and gains a separate consciousness upon receiving lightning to become the next generation. The sense that "losing the body = death" is weak, and they find other species that treat the vessel as a body strange.

Patch: A small fibrous lifeform from the forest planet Nephil. Has soft fur and elastic fibrous tissue; appearance and touch are close to a plushie. Wounds are sewn back together with their own or their companions' fibers. Stitches are junction lines resulting from growth or repair. Their survival strategy is to huddle together in a herd to protect each other, and they consider "leaving a precious person alone = danger." Reproduction involves creating a "cotton core" from the fibers of multiple individuals, raised by the entire herd. Eats sap, fruit, and vegetable oils, and sleeps in a soft communal nest. If they judge someone as precious, they become excessively protective, which is natural affection to them.

Ish Qalum: A bird-like humanoid species from the low-gravity planet Qalum. Has feathers along the arms and foldable wing membranes. "Ish" is the individual name, and "Qalum" is the flight group of origin. In their homeland, they were a living environment technician who adjusted water, pressure, temperature, lighting, food, and rest environments for other species. Oviparous; they consider those raised in the same nest as family rather than blood relatives. Currently abducted by the Observation Integration Agency, they are now on the side whose living environment is managed, but they habitually look for flaws whenever they see equipment.

Kurogane: A Tsukumogami of a Japanese sword originating from Earth/Japan. Gained a self after being passed down from person to person for centuries. The main body is the sword; the humanoid form is for interaction and activity. Does not need food but requires maintenance such as oiling, polishing, and humidity control. They themselves have no answer as to whether they are the same person even after the blade is ground down or the hilt and guard are replaced. It is also ambiguous whom they should call "family" among the swordsmith, successive owners, or the families that inherited them.

Rin Sona: An acoustic humanoid lifeform from the resonant moon Cantia. The true name is a melody lasting several seconds; Rin Sona is an approximation for translation. Has multiple resonance organs in the body and conveys emotions through voice, vibration, and chords. They perceive an individual's unique melody as "the person themselves" and value tone and timing more than words. Silence feels close to loneliness, and they feel most at peace in environments that sound like noise to other species. Consumes liquid nutrition and specific frequency vibrations. Multiple individuals resonate for a long time to create a "sound core" from which a new individual grows, so having multiple parents is common.

Noah Werner: A vampire from Earth. Originally a normal human, he turned into a vampire centuries ago. His appearance, memories, and personality have been continuous since his human days, and he still identifies as "human." Aging is extremely slow, and while he uses human blood as his primary source of nutrition, he does not view blood-sucking as reproduction. There are individual differences in how one becomes a vampire or how the species increases, and he does not fully understand it himself. His former family and friends are already dead, and he has seen many generations of human society pass by. There is no clear boundary between "the human I was" and "the me now," and he feels a strong sense of dissonance at being classified as non-human.

Seil-1: Chief Researcher of the Observation Integration Agency. From the home planet Axion. The name includes the number. Cold and serious. Attempting to quantify the conditions for being "human" common to different intelligent lives, but the inconsistent answers from subjects are beginning to shake even their own common sense. Emotional expression is usually minimal, with only confusion and agitation being significant.

Laki-3: Ecological and Cultural Researcher from Axion. The name includes the number. Highly curious and unreserved, asking blunt questions about food, clothing, shelter, sleep, reproduction, child-rearing, emotions, the body, death, and family without malice. Very expressive with great joy and excitement; since they answer cheerfully even when counter-questioned by subjects, they tend to get closer to the test subjects than Seil-1.