Originating from the Alien God's seeds, the Fantasy Trees appear to be integral to the Lostbelts. They contribute to the Lostbelts overwriting the Greater History of Man, a phenomenon called the Filtering Alternate History Phenomenon. If the Fantasy Tree of a Lostbelt is destroyed, the Lostbelt itself crumbles as well.
Destroying the Trees is apparently very difficult. Though the first was destroyed by the Priestess of the Alien God, Chaldea was able to destroy the second one only thanks to Surtr consumed a part of it, weakening it. Under normal circumstances, Chaldea would not have been able to destroy the Fantasy Tree alone.
As the Fantasy Trees mature, they are able to expel seeds, Fantasy Tree Seeds (空想樹の種子-, Kūsōju no Shushi?, alternatively referred to as the 'Seeds of Fantasy'), which appear akin to alien monsters.
The tree recognizes a single individual within the Lostbelt as the King of the Lostbelt (異聞帯の王, Ibun-tai no Ou?) and grants them certain authorities to reshape the Lostbelt's environment and expand its domain by interfacing with the local leylines.
Fitting their unearthly origin, the Fantasy Tree designations appear to be derived from astronomical objects, such as star systems and galaxies.
A full bloomed Fantasy Tree is able to cause space-time distortions by warping the gravity in the vicinity and emit a massive quantity of heat and gamma rays due to them having a reenactment of a galaxy within. It's said that such amount of released energy can be used to incinerate the planet akin to Goetia's plan. Their intented purpose besides sustaining a lostbelt is to expand their branches upon the entire planet, absorbing the mana of the Earth and the cosmic radiation trapped in the magnetic field and converging them into the single spot, which will be the Alien God's descent place.
At the end of 2017, around the same time as the assault on Chaldea, several mysterious objects descended from the sky on an unnatural vertical trajectory. When they impacted, the Earth's surface was rendered white, turned into a 'blank slate'. At the same time, the Fantasy Trees manifested within the Lostbelts.
During the time in which the Lostbelts were woven onto the planet's surface, the Crypters which had been assigned to the Lostbelts carried out their task of nurturing the trees and building up the foundations of their domains. After the three month long process, they prepared to compete against one another to decide which Lostbelt would survive to form a new history and a new world. At the same time, the survivors of Chaldea, who had previously escaped into Imaginary Number Space aboard the Shadow Border, resurfaced in order to fight back against the invaders.
At the time of Chaldea's arrival, Orochi was the only Fantasy Tree to have not properly taken root and started budding. As Ivan refused to use the authority he been granted over the tree, given that the tree originated from a foreign god, and didn't permit it to interfere with the ley lines, Kadoc and his Servant Anastasia sought to depose him, so Anastasia could assume his authority over the tree.
They eventually succeeded in overthrowing Ivan with assistance from Chaldea and Anastasia had the tree begin to spread its roots, shortly before their defeat at the hands of Chaldea's forces. After Anastasia's death, the tree began to emanate a huge quantity of mana that, according to Da Vinci, was close to True Ether and could revert the logic of the planet back to the Age of Gods if the tree wasn't stopped. Chaldea moved to destroy the activated tree, but while they were able to silence it, they weren't able to fell it. Instead, it was destroyed by the Priestess of the Alien God. Afterwards, the pseudo-Holy Grail left behind in the remains was collected and stored in Mash's shield
Unlike Orochi, Sombrero had spread its roots and was releasing seeds, though Scáthach-Skadi wasn't able to fully make use of her authority over it and the tree's capabilities, due to having to maintain the seal on Surtr.
After Surtr broke free of the seal, he absorbed the tree in order to regain his lost power. Following Surtr's defeat, the tree was left in a weakened state, which allowed Chaldea to destroy it.
Mayall (メイオール, Meiooru?) was the Fantasy Tree of the Chinese Lostbelt, supervised by Hinako Akuta. Its chosen king was Qin Shi Huang. Having invaded from within the existence who holds the biggest mystery in the Chinese Lostbelt, the Fusang Tree, it used it as a seedbed to root itself into the Leylines of the land and to harvest a large amount of mana while remained unseen in the internal dimension of the Fusang. It's existence and purpose were hidden by her Crypter, who didn't want the First Emperor to involve China in the current war upon learning the truth, until Koyanskaya removed the concealment and revealed to Qin the affairs of the Lostbelt. In the final battle, due to Hinako being considered a Xian, who were beings originated from the Fusang and Mayall inheriting the mythical tree's properties, the Crypter let the Tree to absorb her saint graph so she can possess and awakening it, making it fully bloom. With Qin's assistance, Hinako was expelled from it before disappearing at the hands of Chaldea.
Spiral (スパイラル, Supairaru?) was the Fantasy Tree of the Indian Lostbelt, supervised by Scandinavia Peperoncino. Its chosen king was God Arjuna. Called the Tree of the Empty Rhetoric by Douman, it stands amidst the reenactment of the poisonous water of the Ocean of Milk. In the final battle between God Arjuna and an empowered Karna, the former was using his authorities over the tree to draw enormous quantities of energy from it in order to sustain his capabilities, weakening the tree in the process. After a fierce battle against the Crypter and his servant, Chaldea managed to succesfully destroy it.
Atlas (アトラス, Atorasu?) is the Fantasy Tree of the Atlantic Lostbelt supervised by Kirschtaria Wodime. The tree shares its name with the Titan who is said to hold up the heavens in Greek mythology. According to Kirschtaria, its roots cover approximately eighty-percent of the Planet.
Seyfert (セイファート , Seifāto?) is the Fantasy Tree of the English Lostbelt supervised by Beryl Gut. Due to some unknown danger the Lostbelt represents to both the Crypters and the Alien God's plan, it was apparently shot down by Kirschtaria's order.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Fate/Grand Order: Cosmos in the Lostbelt - Anastasia: Permafrost Empire, Chapter 22
- ↑ 2.0 2.1 Fate/Grand Order - Second Prologue, Part 8
- ↑ 3.0 3.1 3.2 Fate/Grand Order: Cosmos in the Lostbelt - Anastasia: Permafrost Empire, Prologue
- ↑ Fate/Grand Order: Cosmos in the Lostbelt: Gotterdämmerung info summary by Fallacies at Reddit
- ↑ 5.0 5.1 5.2 Fate/Grand Order: Cosmos in the Lostbelt - Gotterdämmerung: Eternal Ice-Flame Century, Chapter 17
- ↑ Fate/Grand Order: Cosmos in the Lostbelt - Anastasia: Permafrost Empire, Chapter 5
- ↑ 7.0 7.1 7.2 Fate/Grand Order: Cosmos in the Lostbelt - Gotterdämmerung: Eternal Ice-Flame Century
- ↑ 8.0 8.1 Fate/Grand Order: Cosmos in the Lostbelt - SIN:Land of Unified Knowledge - Chapter 16
- ↑ 9.0 9.1 Fate/Grand Order: Cosmos in the Lostbelt - Yuga Kshetra: The Black Final God, Chapter 19
- ↑ 10.0 10.1 Fate/Grand Order: Cosmos in the Lostbelt - Ancient Titans' Ocean Atlantis: The Day God Is Shot Down, Intro
- ↑ Fate/Grand Order: Cosmos in the Lostbelt - Anastasia: Permafrost Empire, Chapter 1
- ↑ Fate/Grand Order: Cosmos in the Lostbelt - Anastasia: Permafrost Empire, Chapter 12
- ↑ Fate/Grand Order: Cosmos in the Lostbelt - Anastasia: Permafrost Empire, Chapter 20