Shinju (神樹; lit. "Divine Tree") is the agglomeration of earthly gods and some exiled heavenly gods in the universe of Yuki Yuna is a Hero that remains in Jukai. It is stated it chooses girls with high aptitude to fight Vertex. People mainly refer to it as "Shinju-sama" showing their high respect for it as it protects humanity.
The Shinju takes the form of a large tree, whose branches loom high over the Shikoku region. The individual gods within the Shinju have not yet revealed themselves.
When expending its full power, blossoms grow from its branches, mist or fog also encovers the divine tree as well. As a result, the branches and base will disintegrate into black dust.
In the beginning, the heavenly gods and the earthly gods were fighting over the value of humanity. When the heavenly gods won, in July 2015, they sent the Vertex to destroy the humans; however, in response, the earthly gods joined together to form the Shinju and bestow humans with divine power.
The Shinju's barrier was expected to last hundreds of years; however, in the second season of the anime, Aki-Sensei tells Yuki Yuna that the Shinju will soon wither away and all will be consumed by the intense heat outside the barrier. This was due to the heavenly gods' anger in response to humanity's plans to take back the land that was lost, as well as the Shinju's continued loss of power by having to create new bodies for the Heroes to nullify the effects of Sange. To prevent this, Aki-sensei requested Yuna agree to a Shinkon, a sacred wedding, to save humanity. According to her, once the Shinkon is complete, humans will no longer be humans and become "People of God".
The Shinju is assumed to have perished after giving humanity back the world, with Aki-sensei stating "The gods of land have perished."