The current Key identified as Kagari, whose role is central to the storyline.
Keys are born in a place that will emerge a power spot that emits aurora. This power spot is their umbilical cord that connects them to the planet and remains until the Key's death.
Their birth signifies that the planet is running low on aurora. Once they are born, they look into the memories of humanity. They are particularly looking for a good memory, and if they are unable to find it, Salvation will ensue.
Because of their connection to Salvation, they become the center of conflict between Gaia and Guardian, organizations that have conflicting views towards the Key. Summoners unaffiliated with Gaia, the druids, are tasked to protect them.
They use ribbons, attached to both arms, as means of defense. Called Miracle Ribbons, they are made of aurora and is a part of their body. It is capable of multiplying into several strands of ribbons and create a massive wall that is almost impossible to break through. It can also slice through enemies. It can also be used to treat injuries.
In addition, every time a Key is born, a rewrite user is destined to be born prior to their birth.
Keys commonly have young, innocent appearances, with flowing ribbons tied around both arms. They are described to have a scent of earth. They also tend to be hidden from view of most people.
Kagari has deep lavender-coloured eyes and a ribbon is tied onto both her wrists. In Harvest Festa, she wears a normal school girl attire.
Main article: Kagari
- Invisibility: Some people are unable to see Kagari therefore, she is able to stand in the midst of a battle and not worry about being attacked. In the forest, she was completely invisible to the enemy while Kotarou and Mosu's lives were in danger. However, Kagari's invisibility only works as long as she is conscious, if she is rendered unconscious she can be seen by anyone.
- Singing: Kagari can sing a strange tune (namely the Song of Destruction) that is said to be hard for humans to understand, Kotori stated that when the Key/Kagari starts to sing salvation is approaching.
- Magma Flames: The moon Kagari seemingly killed Kotarou once by setting him on fire.
- Vortex: When Kagari learned that Kotarou had exposed himself to Sakura Kashima to save Akane and Tsukuno, Kagari threw a tantrum; her ribbons turned razor-sharp and created a destructive cyclone around her.
- Husk: (Shizuru Route) Once the Key stabilizes, a shell is produced, which is practically invincible, evidently, bullets are powerless against it, the hull is identical to Kagari. It is very difficult to destroy the Husk, though Touka Nishikujou was able to extirpate it by using her own body, resulting in her death, however, salvation perpetuated and persisted to decimate the world.