Fantasy Tree

A Fantasy Tree (空想樹, Kūsōju) is a kind of mysterious tree-like construct which sustains a Lostbelt, appearing in Fate/Grand Order: Cosmos in the Lostbelt as its final bosses in each of the seven chapters.

For now, four of the known Fantasy Trees had their name revealed; Orochi (in the Russian Lostbelt), Sombrero (in the Norse Lostbelt), Mayall (in the Chinese Lostbelt) and Atlas (in the Atlantic/Greek Lostbelt).

Overview
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.

The trees are extremely tall, extending far above the clouds and up through the stratosphere. Due to their immense height, they have also been referred to by the term Cloud Tree. As the Fantasy Trees mature, they are able to expel seeds, Fantasy Tree Seeds (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 Lostbelt King and grants them certain authorities to reshape the Lostbelt's environment and expand its domain by interfacing with the local leylines. For now, three Lostbelt Kings were surfaced.
 * 1) Tsar Ivan IV of Russia, also known as Ivan the Terrible, who was constructed into the very first Yaga after his Lostbelt was hit by an asteroid, in order to survive the subsquent Ice Age. the Tsar had postponed the landing of Orochi, the Fantasy Tree of Russia. Kadoc, one of the Crypters, attempted to take control over the Lostbelt by hailing his Servant, Anastasia, as the new monarch, before making the Fantasy Tree rooted and expand its Lostbelt.
 * 2) Scathach-Skadi, who was the Norse Goddess Skadi merged with the Lostbelt version of Scathach by a dying Odin, who sealed Surtr and stopped Ragnarok from ever happening in order to save humanity. Unlike the previous Fantasy Tree, the Fantasy Tree in this Lostbelt already rooted but was hidden.
 * 3) Emperor Qin Shi Huang, who reached immortality at the year when he supposed to die, and became the eternal ruler of Chinese Lostbelt, developing powerful technology for his palace as well as a nigh-utopia for his citizens. However, the Emperor showed no interest in assisting the Alien God. Instead, he fought against them and the Crypters while fixing humanity for himself, even sealing his Fantasy Tree.

Fitting their unearthly origin, the Fantasy Tree designations appear to be derived from astronomical objects, such as star systems and galaxies.

History
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.

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 Sutr consumed a part of it, weakening it. The third one was merged with Consort Yu and became matured, but was destroyed with the help of Emperor Qin Shi Huang.

Under normal circumstances, Chaldea would not have been able to destroy the Fantasy Tree alone.

Source

 * This article uses material from the Fantasy Tree on the TYPE-MOON wiki at Wikia and is licensed under the Creative Commons Attribution-Share Alike License.