The Azure Tree (碧の大樹,Ao no Taiju?) is an enormous, magical structure that appears in Ao no Kiseki. Described as the Azure Teasure (碧の至宝,Azure Teasure?), it is KeA's evolution of the Zero Treasure (零の至宝,Zero Treasure?), as being the final phase of The Zero Project (零の計画,Zero no Keikaku?)
The interior of the Azure Tree is comprised of different territories, which include The Sanctuary, the cavernous Territory of Shou, the garden-like Territory of Siki, the hellish Territory of Gou and the chained labyrinth Territory of Kai. The final chamber, The Farthest, is where KeA is held captive and where the Azure Demiurge is fought.