In the world of Crystan, countries are constantly at war with each other and had never reached a conclusion. Bloom Salutori is a girl with amnesia who meets with two men who could change her future, Kazu Gespenst the Blind Joker, and Lloyd Freedom the Holy Berserker. Bloom will go on a quest to decide her future and put an end to the Eternal War, and in her adventure, she meets Siegfried Sonata, a criminal known as "Black Blade" and a sign of hope for the kingdom of Xopolis known as the "Lost Prince", and Amy Bladia, the princess of a forgotten kingdom in Victoria. As her quest continues, Bloom must decide on the way she wishes to create the utopia she longs for, the way of tyranny or the way of peace.
The Eternal Tale has an real-timeaction-based battle system where normal attacks will happen automatically when enemies enter a party member's attack radius, similar to The Last Story's battle system. However, manually-activated special attacks, called Talents, each have their own "Cooldown" time after being used. Talents for each character have to be set on a "battle palette" at the bottom of the screen, which can be modified outside of battle. Movement of the character in play is also executed manually with the analog stick and could change the advantages and disadvantages of the battle.
The game have save points scattered through out the game in places before the key points of the story and in inns. The save points are shown as glowing cyan discs making them easier to notice, they also appear in the maps which also reveals where all saving points are in the current stage. Checkpoints can be made at any time in the game, but a checkpoint can only be used once per loss and will be lost until the player resets the checkpoint.
Another of the game's systems is the "route system", in which the player is allowed to partake in side-quests and increase the percentage of the Dark or Light routes. The Dark or Light routes will determine the ending of the game and decide which side will Bloom end with. Partaking in the side-quests will also help the characters gain experience depending on the difficultly level of the side-quest.
The game also has extensive customization, such as being able to change the character's outfits and having those changes be seen during battle, in the field, and even during some event scenes. Most character outfits could be edited in the color menu of the pause menu.
The game also features online multiplayer modes where up to 12 players can choose any character from the game to play with other players; Alliance, players team up to take on a boss for special rewards, War, two teams battle with each other with their own small armies of six players and four NPCs, and Melee, a player vs player battle royal mode which allows multiple players to fight each other using any character from the game that can fight.
- Bloom Salutori - A girl with amnesia who wishes to create a utopia and doesn't really care for her old memories. She uses sword named "Memory".
- Siegfried (Sieg) Sonata - A criminal and prince nicknamed "Black Blade" who leads a rebellion against his father, the king of Xopolis. He uses a cursed sword named "Crow".
- Amy Bladia - A mysterious girl who wishes to revive the lost kingdom once known as the Sword Kingdom. She uses a sword named "Red Rabbit".
- Kazu Gespenst - A blind mage who leads Bloom towards the Dark Route.
- Lloyd Freedom - A rogue paladin who leads Bloom towards the Light Route.