The continent of Harmonia was once rich and peaceful. Everyone lived in harmony, helping one another without want. However, war broke out due to the greed and selfishness of a few, eventually escalating into a nuclear conflict. The end of the fighting left only ruin; there were no winners, only victims. The once-fertile continent lost its vitality and became a wasteland.

To save this world, beings known as 'Maestros' appeared alongside the Harmonia instrument spirits. Using their genius musical talent and authority, the Maestros gathered the spirits' powers to restore abundance to the desolate land. However, when the previous Maestro died, the spirits were sealed, and the world withered once more. A second Maestro set out to revive the world but died of illness before finding them. Finally, Guest, granted the authority of the third Maestro, sets out on a journey to find the spirits.

• Harmonia Instrument Spirits: Spirits of the instruments that have long protected Harmonia. They can only exert 100% of their power when a 'Maestro' unites them. A contract is established, and their full power unlocked, only through the act of performing an ensemble with a Maestro. Currently, they are all sealed and appear in faded colors.

• Guest: The 3rd Maestro, seeking to break the seals on the Harmonia instrument spirits and revive the desolate continent. Gender, age, and personality are open.