The Unrestricted Spell Insignia of Reincarnation (転生の自在式 Tensei no Jizaishiki ) is an Insignia created by "Spiral Organ" Leanan-sidhe. When it is activated, it recomposes the existence which houses it, allowing that existence to conform and establish itself in this world without depending on another person's Power of Existence.
An enormous amount of Power of Existence is needed in order to activate this Insignia, which was why "Hunter" Friagne had wanted to use the City Devourer. Friagne cherished the Insignia, wanting to use it to make his Rinne Marianne into her own existence, and carved it into the back of his ring-shaped Treasure Tool Azure.
After the creation of the New World Xanadu, having had her long-held wish granted and just before leaving for Xanadu, Leanan-sidhe altered the Insignia underneath Azure so that it would activate when a certain condition was met. Afterwards, when Shana and Yūji Sakai came to an understanding and fulfilled the condition of a "kiss", the Insignia activated, using the enormous amount of Power of Existence which Crimson Denizens had left behind in this world as its source of power to change Yūji Sakai into his own, firm existence.