The Yggdrasil Project is a group of scientists who created the Seven Yggdrasil Trees (not including the Deep City, Arcanian, or Amber Yggdrasils), and thus saved the planet Earth and the human race from the apocalypse. These scientists were the ancestors of the Imperial culture.
However, this ability came at a price. While the Yggdrasils were capable of absorbing the pollution that had tainted the world, the project was put into motion before all safety protocols could be safely established due to the deteriorating state of the world. Without the appropriate safety protocols, the Yggdrasils could, after long enough, go berserk from absorbing all the pollution and begin to unleash it back onto the world. As a result, various alternate failsafes were created to attempt to destroy the Yggdrasil in each location should the worst case scenario happen.
In Etrian Odyssey Untold: The Millennium Girl, with the expansion of the story behind the Yggdrasil, two failsafes were detailed. The Gungnir unit is a weapon of mass destruction capable of destroying the Core, but with the drawback of annihilating everything and everyone in the vicinity. One in the nearby city of Gotham had successfully activated, and the plot of Untold revolves around trying to destroy the Core at Etria without necessitating the Gungnir unit. To do this, the Yggdra Virus, designed to destroy the Core, was created and held by Visil, and was acquired by the party in order to save Etria. However, the Virus failed to kill the Core, and the party was only able to succeed in killing it with Kupala's soul powering them up (though the Yggdra Virus might have rendered the Core unable to regenerate more than once).
In Etrian Odyssey 2 Untold: The Fafnir Knight, the Yggdrasil Core is central to Ginnungagap and the Fafnir's story. For generations the Fafnir had maintained a seal over the Yggdrasil Core to prevent the Calamity from occurring again, while the Overlord, in his floating castle, worked endlessly on the Holy Grail to find a way to destroy the core. It is only due to the anomaly that set the story's events in motion that the party is forced to find a way to destroy the Core for good.
In Etrian Odyssey IV: Legends of the Titan, the Yggdrasil's power manifests in the ability to force vegetation to grow nearly anywhere - even in individuals. This affliction is known as the "Titan's Curse", and only the Medium can reverse this. Prince Baldur, and his father before him, sought to make use of the Yggdrasil's power to restore life to their now-barren lands, with the Prince going so far as to awaken the Heavenbringer despite knowing that doing so will condemn both the Vessels and Sentinels to a death by the Curse.
In addition to this, the notes found scattered across the Hall of Darkness detail an "insect" designed to eat the Imperial Yggdrasil should it go berserk. However, the tree's power had corrupted the failsafe, turning it into the Warped Savior, and forcing the scientists to lock it away in the depths of the complex. While attempting to contain the creature, they proceeded to develop a series of chemicals designed to weaken it, but the last of the scientists died before they could finish the chemical sequence, leaving just enough hints in the form of containment notes scattered around the Hall for the party to deduce the means to complete it.
So far, three of the Yggdrasil Trees (the Gotham, Etrian, and Lagaardian ones) have died, and the Tharsis Yggdrasil has been deactivated again (though with Medium Xiuan still alive, the Heavenbringer has the potential to return, as seen in her dreams where the player can fight the Titan multiple times). Three other Yggdrasils remain at large - it is unknown if the Yggdrasil in Etrian Odyssey III or the one in Etrian Odyssey V have any ties to the Yggdrasil Project.
- Frederica Irving
- Frederica's father
- Black Guardian
- Researcher who created the chemical compound that would weaken the Warped Savior