The game is centered on the Polish romantic pianist and composer Frédéric Chopin, who died of tuberculosis at the age of 39. 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. The game features a selection of Chopin's compositions played by pianist Stanislav Bunin, though most of the in-game music was composed by Motoi Sakuraba. The game's battle system centers on musical elements and character-unique special attacks. Light and darkness plays a part in the appearance and abilities of enemies on the battlefield, as well as the types of magic that can be cast.

Gameplay

Eternal Sonata follows many general conventions in a typical console role-playing game: the player controls a party of up to twelve characters to explore the world, talking with its inhabitants, buying and selling equipment at shops, and encountering monsters while in the field. These encounters are visible, and the player can opt to avoid the encounter, if possible, as well as gaining an edge on the monsters by approaching them from behind. Experience points are awarded to all members of the party, though at a reduced rate for those not involved in combat, and characters will improve in various statistics with each experience level as well as learning special combat skills. Weapons, armor, and accessories can be used to improve these statistics, which can be purchased through money earned in combat, found in chests, or by selling both equipment and photographs which can be taken by the character Beat during battle. The player may also find Score Pieces scattered about the world, which represent short musical phrases. Various NPCs in the game will offer to perform with the party, requiring the player to match a Score Piece to the phrase offered by the NPC, with the resulting composition being ranked. Discordant matches will result in no reward, but close or perfect matches will gain a bonus item from the NPC.

Combat

Light and dark areas on the battle field generated by the time of day, environment, and shadows of the characters and monsters will affect combat. Each party character has one or more special skills that are active in lit areas, and a similar number but with very different effects in a dark area. Monsters themselves may have a dissimilar set of powers in the area of the battlefield they are in, while other monsters will actually change form when they move between lit and dark areas. The player can manipulate the nature of areas using special items, but this can also be affected by the monsters themselves, or through dynamic changes on the battlefield such as the shadow of a cloud moving across the ground.

As the player progresses through the game, they will increase their Party Class Level. Each improvement in level grants some bonuses while also imposing additional limits on combat. For example, one Party Class improvement increases the number of slots for special skills for each character, but at the same time, cuts down the amount of Tactical Time and time available in the Action Gauge.