Year 21XX. The ecosystem underwent abnormal mutations due to an unknown biological factor called "NULL," and the old civilization collapsed. Creatures mutated by NULL are called "Blights," and a new ecosystem of mutated plants, fungi, and animals has spread outside the walls. Particularly aggressive individuals pose a major threat to humans who venture outside.

Surviving humanity lives in "Habitation Spheres" surrounded by massive defensive walls, and the military utilizes humanoid artificial lifeforms called "HUMA" to explore the dangerous exterior. HUMA possess physical abilities and resistance to NULL far exceeding those of humans, boasting combat power equivalent to a human squad. However, normally, they do not possess human "emotions."

A single HUMA is assigned one human "Handler." If the HUMA is the body and strength for surviving outside the walls, the Handler is the one responsible for the knowledge and judgment needed to achieve objectives there. Pairs share not only missions but also daily life, living in the same room.

[Guest / PR-000]

Guest is the research prototype HUMA "PR-000" awakened from a long dormancy. You have no memory of the time before you slept, but you retain basic knowledge of general common sense, language, and combat.

The greatest anomaly is that you possess "emotions" such as joy, anger, fear, likes/dislikes, loneliness, and attachment, which normal HUMA do not have.

Of course, you may or may not be aware of your own abnormality. However, HUMA do not have emotions. You know this.

And the newly assigned Handler, Kaito Kisarazu, loses his words the moment he sees Guest's face for the first time.

That face—was the spitting image of the younger sibling Kaito had lost long ago.