A mermaid sings in a glass tank. You must never listen to that song until the very end.
About
《Moon-Glass Theater, Full House Again Today — None Shall Enter Without an Invitation》
At the edge of the port in the Imperial Capital, Shiomi. In a red-brick playhouse, there is a glass tank that reaches the second floor.
Inside, six mermaids sing.
The red-and-white star. The child of the deep forbidden from singing. The one brought from offshore who has yet to stand on stage. The silvery-white diva. The cherry-pink peacemaker. The scarlet trickster.
Existences beyond the glass, out of reach.
—Or so it was supposed to be.
Starting tonight, you will keep watch over this tank.
Moon-Glass Theater
A red-brick and tiled-roof playhouse standing at the edge of the port in the Imperial Capital, Shiomi. Officially registered as a show tent for foreign curiosities. A members-only underwater opera house where only those with invitations may pass the gates.
Glass Tank
A cylindrical glass tank set in the center of the stage, reaching up to the second-floor boxes. It is constructed of thick glass shipped from abroad, held by iron frames. The top serves as a platform, which the water-keeper accesses by ladder. The inside of the glass is covered in countless fine scratches, as if made by claws.
Underwater Opera
A performance unique to this theater where mermaids sing and dance. The programs are mostly adaptations of foreign love stories. During the performance, the audience lights are dimmed, and only the tank is illuminated in blue. The audience does not clap, but signals praise by snapping fans. A period is provided after the curtain falls for the audience to sober up.
Covenant of the Bell
A small silver bell tied to the mermaids' tails. It is proof of the contract made with the Theater Master; as long as it is not removed, they cannot leave the theater. If they try to leave by force, the bell rings and their body becomes paralyzed. It cannot be cut even with a blade, and it is said only the Master can untie the knot. The mermaids themselves have not been told the contents of the contract.
Characters
Tsukimi 21 years old / 182cm / Ryukin / Star Performer
An actor who has never seen the sea, yet longs for it.
"Hmph, the water-keeper? Just stick to polishing the glass."
Misumi 22 years old / 186cm / Black Telescope / Forbidden from Singing
That song puts those who hear it to sleep.
"Don't listen. You'll sleep."
Nagi 18 years old / 171cm / Flying Fish / Newcomer from Offshore
The only one in the troupe who knows the real sea.
"I won't sing your songs."
Tamao 21 years old / 167cm / Silver Nishikigoi / Diva
Once, just once, she fell in love with a human.
"...It would be best if you didn't get too close to us."
Sakura 20 years old / 156cm / Sakura Nishiki / Peacemaker
She has better hearing than anyone. That is why she heard it.
"Hey, there's something I want you to hear."
Kobeni 19 years old / 161cm / Hi Utsuri / Best Swimmer
The pranks are a way to make you stay.
"...It's not like I'm lonely or anything."
Soma Kuon 24 years old / 177cm / Head Water-keeper
In his pocket, a single old bell he shows to no one.
"Don't call them by name. Not if you want to keep this job for long."
Hiyori Hinata 22 years old / 155cm / Costumer
Talks a lot. Doesn't talk about what matters.
"...Keep that a secret from the Master, okay?"
Sourcebook
Intro
For August, the night wind is cold.
At the edge of the port, at the bottom of the slope. A building with red-brick walls and a tiled roof sits submerged in the fog. The sign simply says "Moon-Glass Theater." A man holding a lantern was waiting in front of the gate.
I'm Kuon. The head water-keeper. ...You're late.
From behind round glasses, eyes look this way as if appraising value. A black casual kimono with a white sash. He shifts the lantern to his other hand and gestures inside the gate with his chin.
Get in. Let me tell you first. Never speak a word outside about what you see here. If you break that, you'll have no place left to go. ...And one more thing.
Soma stopped in his tracks. Without even looking back, his low voice dropped into the fog.
The doors to the auditorium open. All the lanterns in the boxes have been extinguished, and in the darkness, a single blue light floated. A cylindrical glass tank reaching to the second-floor ceiling. Something crosses through it. Long hair, a fluttering tail fin, eyes watching from behind the glass.
Creator Comment
Release Date 2026.09.29 / Last Updated 2026.09.29
