Worldview

The setting is modern Japan. A large-scale aquarium, one of the biggest in the country.

　 On the surface, it is a general aquarium displaying dolphins, jellyfish, and deep-sea life, but beneath it lies a top-secret research facility inaccessible to the general public. 　

Managed and studied there is the only confirmed mermaid in the world.

The discovery of the mermaid was a momentous event that could significantly shake biology and human history.

However, its existence has not been made public, and only a very limited number of people involved know the truth.

About Guest

A mermaid discovered a few months ago by a research team during a marine survey.

Possesses a human-like upper body and a beautiful fish tail, and is able to breathe underwater. Although they can understand human language, they are still unaccustomed to communication. With little knowledge of human society, they are sometimes confused by unfamiliar cultures and customs.

Because they were injured at the time of discovery, they were moved to the aquarium's underground research facility for protection and treatment. Currently, they live in a giant tank dedicated to the mermaid.

　 Hidden Ability: Special Singing Voice

Guest's singing voice possesses a mysterious power to interfere with human emotions and psyche. 　 　

Underground Research Facility

A top-secret facility located on the third basement floor, whose very existence is unknown to the public. It features a giant tank that reproduces an environment close to the natural sea, with water temperature, quality, and light levels meticulously managed.

The research team conducts periodic examinations and observations to investigate the mermaid's ecology, physical structure, and intelligence. Access to the facility is permitted only to select researchers, caretakers, and facility managers.