Around midnight, the train pulled to a stop beside a ruined cathedral.
The moment the doors opened, a low chorus came flooding in. The language was ancient, but the melody itself vibrated deep in their bones.
"It’s the Observers’ Hymn," Kuon said, his face tightening. "This isn't a song to boost morale. It’s a synchronization spell. Listen to it long enough, and it will erode your own sense of judgment."
Asahi tore strips of cloth to use as earplugs and handed some to Koyoi.
Yet, the song still reached them—not as sound, but as a vibration that seeped directly into their bodies. The closer they drew to the cathedral, the more their strides were pulled into the song’s tempo. Three steps forward, a one-beat pause. The sense of walking by their own will began to fade.
Koyoi clutched her pouch, counting the rhythm of the droplets within to overwrite the hymn’s pulse. One, two, three, four. She etched a different beat into her own body.
Inside the cathedral stood about a dozen Observers. They formed a ring of black robes, all fixed on the same sheet of music. At the center stood a pillar of pale light.
"That pillar is the synchronization core," Kuon whispered. "Even if we stop the choir, it will just start again as long as the pillar remains."
Asahi drew her sword. "Then I’ll cut it down."
"A direct assault won't work," Kuon warned. "The song is forcing your blade to match its timing."
Koyoi looked at the edge of the score. The ink was blurred in places, with notes scrawled by a different hand—instructions to shift the time signature.
"Someone altered this part," she said. "The synchronization isn't perfect."
Kuon reacted instantly. "We can use that fluctuation. Koyoi, insert a counter-beat on the fourth count."
Asahi circled to the right of the pillar while Kuon opened his lexicon, tracking the hymn’s cadence across the pages. Koyoi took a breath and found her voice, matching it to the rhythm of the droplets.
A sharp exhale. She drove only the fourth beat hard, throwing it out of sync with the hymn.
The circle of the chorus wavered. One, then two voices fell out of tune.
In that instant, Asahi lunged. Her blade didn't strike the pillar, but the musical staff lines carved into the floor. She severed the engraved symbols.
The pillar’s light flickered. Kuon tore a page from his book and hurled it, pinning it to the base of the light. A spell-circuit flared to life, and the pillar’s synchronization broke.
Finally, Koyoi pressed the pouch’s warmth into the disrupted spell. The cold light softened for a moment, then thinned and vanished.
The chorus fell silent. The Observers looked at one another in confusion. The moment they lost their shared song, their strides became disjointed and erratic.
"Retreat," Kuon said curtly. "There’s no need to make enemies of them all right now."
The three left the cathedral and headed back to the train. Behind them, someone began to hum a faint, different melody. It wasn't a song of command. It was a personal song.
Koyoi didn’t look back, but she committed the melody to memory. She knew that what remained after breaking the synchronization would be a clue to the next age.
Even after returning to the carriage, a low resonance lingered in Koyoi’s ears.
Asahi removed her earplugs and asked, "Can you still hear it?"
"Yeah. But it doesn't sound like an order anymore. It's just... someone's ordinary song."
Kuon made a brief entry in his lexicon: “Individual melodies confirmed following severing of synchronization.”
It was a small record. But it was the first clue left behind after unraveling the great hymn.