The Sacred Tree is a magical tree located in the center of the Fairy King's Forest, which acts as a portal between the human realm and the fairy realm.
The Sacred Tree exists in the heart of the Fairy King Forest. According to King, the Tree exists to protect the Fairy Realm and has no feeling of evil. Fairies live linked to the Sacred Tree and its magic, and some even are born from it.
According to the Lady of the Lake, the Sacred Tree was the third offspring created by Chaos, being the youngest "sibling" to the Demon King and the Supreme Deity. The Sacred Tree then created the Fairy Realm and the Fairy Clan.
The Sacred Tree is the one that chooses the fairy that bears the title of the Fairy King, the one that reigns and protects the entire Fairy Clan.
After an unknown amount of time after creating the Fairy Realm and the Fairy Folk,The Sacred Tree thus then selected Gloxinia as the first ever Fairy King and presumably gave him his Sacred Spear Basquias.
After Gloxinia defection to the Demon Clan as one of the Ten Commandments during the Ancient Holy War 3,000 years ago and his eventual defeat and being sealed in the Coffin of Eternal Darkness. The Sacred Tree thus then selected Dahlia as the Second Fairy King as Gloxinia's replacement. After an unknown amount of time and Dahlia's eventual passing the Sacred Tree thus then selected Harlequin as his replacement as the Third Fairy King and current ruler of the Fairy Clan.
The Sacred Tree possesses an enormous magical power. Some fairies are able to access this power and use it, even summon and control its roots and branches in combat. The Tree is extremely resistant, weapons forged from it are more resistant than steel.
The Sacred Tree possesses many unique qualities. It is capable of emitting healing pollen when it is injured, which also provides protection. The moss that grows in it is capable of shapeshifting into sentinel beings that fight to protect it from enemies. In its highest branches grow the flower known as Sunflower, which can emit powerful rays of solar energy. From the Sunflower is extracted an ivy named Death Thorn, from which the slightest cut seems to result in death. The Spirit Spears possessed by the Fairy Kings possess several of these qualities, which are extracted by the power Disaster.
And given the fact that the Sacred Tree is also a direct creation of Chaos and being the youngest "sibling" to the Demon King and Supreme Deity and it being creator of the Fairy Realm and Fairy Folk Race, the Sacred Tree also likely holds godlike power at the same level as its older "Siblings".