Eternal Sonata is an RPG, developed by tri-Crescendo. The game is about the final hours of legendary Polish composer, Frédéric François Chopin. The story envisions a fictional world dreamed by Chopin during his last hours that is influenced by Chopin's life and music, and in which he himself is a playable character, among others.

An astra is a jewel that is found within the heart of every person in the world of Eternal Sonata. The playable character Polka has an astra that glows brighter than anyone elses in the entire world, and which causes agogos to glow when they gather around her. Astra was mentioned briefly in the original XBox 360 version of Eternal Sonata, but was featured in much greater detail in the expanded PlayStation 3 version.

• That the names of the pirate captain Dolce's Special Attacks change in the final battle against her and her lieutenants?
• That in the English-language version of Eternal Sonata, March and Salsa share the voice actress?
• That the battle theme "Unbalanced," used for the battle with Ruined Body (Waltz and Ruined Body in PS3) is reused for the battle with Annihilator, the final boss of Mysterious Unison?
• That in the PS3 version of Eternal Sonata, Serenade has the highest speed stat of any character, and her exclusive armor Noble White increases it by a further 20%?
• Other than certain of Crescendo's shields, accessories are never found at shops, and with the exception of these and those involved within the trading quest, only a single one of each may be obtained in each playthrough?