The Key is a dangerous familiar in the form of a young girl. In her route, which are the last concluding arcs of the game, Moon and Terra, she is identified as Kagari(Main Article) also see: Terra Kagari and Moon Kagari. Though it may not seem like it initially, Kagari is the main heroine of Rewrite.
Kagari's existence was born at the Harvest Festival, for that reason she occasionally visits her birthplace, evidently Akane informs Kotarou the Key always feels the need to return to its birthplace. Her first appearance is at the end of the Common Route, where her silhouette is projected on the moon. Kagari provides some assistance to the Occult Research Society Club by causing a tree to collapse on the dragon, though whether she intended to aid Kotarou and the others or not is unknown.
Personality
She is very cold and distant to humans, however its very possible that the Key does understand human language at a certain level. It's indicated in Kotori's route that she has a quick temper, for whenever Kotarou gets on her nerves, she uses the ribbons permanently tied on her wrists to her advantage and beats up Kotarou. Her eyes are depicted as emotionless and lacking humanity. She often has the same facial expression signifying calmness and leniet.
Appearance
Although she is not human but a Familiar she looks like a young highschool girl age looking girl, her hair is pale, white and short, and is perceived to be wearing a black dress and hairpin shaped like crosses. 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.
Miracle Ribbons
A source of defense as well as combat. The Miracle Ribbons are actually made of aurora , she can make a decision to conflict harm onto anyone at will, but it does automatically protect her. The Key does not hesitate to attack someone with the Miracle Ribbons, if they seem like even a minor threat, or if they are merely a nuiscance. They are capable of multiplying into several strands of ribbons in order to create a seemingly massive wall, that is almost impossible to break through, Kotarou himself failed to do this when attempting to do so.
Story (Common Route)
While her role is initially minor, the second half of the game focuses on her. With the exception of the last two concluding arcs of Rewrite, Kagari has the most exceeding portion dedicated to her in Kotori's route, however, all the heroines routes are somehow related to the demolition and elimination of the key, which Kagari is referred to as in the first commencing part of the game. Her goal is to witness good memories, if not, as a consequence she will destroy the world without hesitation, resulting in intelligent life starting anew, there is no prevention of this outcome. She is the main cause of the affray between Gaia and Guardian.
Abilities
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 invisable 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.
The Key (Kagari) singing the deadly Song of Destruction
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 si
Kagari in 'Vortex Mode'
ng 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; he 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 invinsible, 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 exterpate it by using her own body, resulting in her death, however salvation perpetuated and persisted to decimate the world.
