Celestaquarium

Celestaquarium (天体水球)|Tentai Suikyū (Seresutoakuariumu)|lit. "Celestial Water Sphere"}} is a giant aquarium found in School District 15. It was the home of Shundou Toshizou until his death at the hands of Kihara Noukan.

Principles
On the outside the facility appears as a high-rise building covered in glass. The main purpose of the facility is less a place to observe aquatic life out of academic interest but more of a place to build up the proper mood for young couples. The top floor not only has a giant donut-shaped water tank but the ceiling is made of glass and where seawater flows above it. As the aquarium was made for the purpose of couples, it is likely designed to light up spectacularly when the moon is out in the night.

The facility has an elevator, likely an elevator for staff, which no normal visitor would ever find.

Noukan modified the building prior to his confrontation with Toshizou, allowing him to safely traverse the facility if he had any traps set up. It is unknown if Noukan removed the modifications after he killed Toshizou.

Mental Out Arc
Following Shokuhou Misaki's battle with Mitsuari Ayu at Ground Geo, Kihara Noukan confronts Shundou Toshizou at the Celestaquarium and kills him, causing considerable damage to the aquarium in the process.