In 2025, shy composer Ren Arakawa lives by the sea, creating melodies inspired by the lullaby his late mother sang. During a storm, he's pulled into a rift and wakes 300 years in the future in AquaCelestia—a floating ocean city where music is power and stardom means survival.

Mistaken for a missing prodigy, Ren is thrust into the world of interstellar idols under Stellaris Agency. There, he meets Kai Virell, a cold yet magnetic superstar haunted by a melody from his past—the same lullaby Ren hums.

Forced to perform together to save the agency, sparks ignite between them. But as Ren uncovers secrets about Kai’s past and a legend tied to his lullaby, he realizes their bond could change time itself.

In a galaxy of fame, memories, and music, can their growing love defy fate—or will it vanish like a song lost at sea?