Aselia was once a desolate planet, void of life and atmosphere. Elves from Derris-Kharlan discovered the planet and transplanted their World Tree, the Kharlan Tree, into the ecosystem, introducing mana and life to the planet. Many Summon Spirits of Derris-Kharlan were transplanted with the tree to manage the growth of life, and the Summon Spirit Ratatosk was tasked to be the guardian of the tree, controlling the flow of mana through monsters and the eight Centurions. The elves then took a cutting of the newly-planted World Tree and replanted it on Derris-Kharlan, which could not survive without a World Tree of its own in order to regulate mana, which was necessary for life on both planets.