Taking place in a futuristic society where there are signs of both primitive and advanced technology, Eternal Legacy begins with two young men from an unnamed rebellion, Astrian and Taric, sets out to steal a Varsh stone in a royal fighting arena in an attempt to rob the supercity of Algoad some crucial electrical power. However, the plan is foiled when another man named Reinherz took the stone for himself. Taric and Astrian attempt to pursue Reinherz but stopped by to rescue Lysty, who was cornered by some monsters. The threesome then chased Reinherz, even when Taric was captured by Aload authorities. Reinherz, he summoned a monster to cover his retreat, and Astrian was injured in the fight against the monster.
Astrian wakes up to find himself in Algoad's governmental residence. It turns out that Lysty was the daughter of Magnate Frey, and was also betrothed to General Gail, Algoad's military leader. Astrian leaves the residence immediately to return to home base to plan for rescuing Taric, with Lysty joining him out of curiosity for the outside world. Upon returning home Astrian teams up with Shira, Taric's sister.
The threesome took off to the volcanic area where prisoners are sent to work, and it was here that Shira learns of Lysty's background. However Lysty convinces the team that she has turned over a new leaf and is willing to help. The team finds Taric, but had to fight him first to detoxify him from some drugs infused by the Algoad authorities. Returning back home, the team finds and rescues an injured bounty hunter named Edmund.
Meanwhile, Astrian had dreams about his past and his parents (that he doesn't know about)
. The dreams tell him to continue to find the Varsh stones and find a place known as the "Oracle's Temple". The temple is far away, but Edmund tells the team that he's willing to help escort them there if they retrieve his airship that was taken by Algoad police. They manage to, but was halted by General Gail. Gail was about to land a killing blow by Astrian but was saved in the last second by Lysty. She renounces her betrothal to Gail and leaves with the team.
The team arrives near the Oracle's temple and now get the true sense of the conflict. Astrian and Lysty were descendants of the Guardians, a group who swore to protect the Varsh stones. These stones, as told by wolf sage Qaniit, were meant to keep away Moon, an evil entity of chaos and destruction. The danger is that Algoad's use of the stones for electrical energy is decreasing the stones' power in turn, allowing Moon to return to Earth and cause Havok. When asked how the stones were taken in the first place, Qaniit talked about The Hunt, a military campaign by Magnate Frey to oust the Guardians and take the stones. Qaniit further explains that Lysty's mother was a Guardian who denied her responsibilities and told Frey about the stones. Frey, then a senator, launched the successful military campaign that promoted him to magnate and influential character of Algoad.
The team (which now included Qaniit) went back to Algoad and attempted to stop Moon from being reborn. However, they were stopped by both Magnate Frey and General Gail. Frey was then possessed by Moon, causing him to kill Lysty. The group was hard hit by the loss, but had to soldier on to find the last Varsh stone when realizing that Moon was now fully reborn. They go the Grand Forest, take the last Varsh stone, and bumped into Reinherz. It was discovered that Reinherz was Astrian's uncle, not father (which Astrian originally thought) and he tried to shield Astrian away from his origins to keep him away from trouble. Although Astrian was bitter of Reinherz's decision, the two ultimately reconcile.
Finally, the team caught up with Moon and Magnate Frey. They free Frey, who in turn committed suicide when he learnt that he killed his own daughter. The team commenced to slay Moon, causing the floating floor around them to crumble and break. The game ends with a shot of the entire team crash landing in a forest without major injuries.
Much like some RPGs, Eternal Legacy sports an open world where characters can explore and accept side quests. Sometimes there are venders that will sell armor and other consumables. There is an arrow that points the character to the main objective of the game.
Characters can equip armor, but can also add fragments to these pieces of equipment. The fragments either add a special ability or provides a passive bonus (like adding more attack). Depending on the situation, players can ride on piyagis (beasts) to speed up travel or use Edmund's airship to arrive at different faraway locations.
Combat involves three player characters, two of which are controlled by the game AI. These characters can follow certain behaviors to suit the likings of the player. The last character, the one character that is manually controlled by the player, has a bar. When the bar is full, the character can perform an action, be it an attack, a spell or an item. Spells, that cost energy to cast, are usually broken down to healing spells and offensive spells (causing damage or other negative conditions). Conditions include, but are not limited to, poison, confusion and paralysis. Moreover, when another bar is filled, characters can unleash a super move that usually cause more damage than an average attack. Also note that full control of the team is optional in the menu screen.