Exta is a spider-like Yin-Self Horror which is one of the nine Horrors freed from the slate that uses their malice to seal the legendary Horror Eyrith. This Horror loves to deceive her victims with disguises before devouring them.
Exta is freed from the the Ady Slate when a mysterious person destroys the slate using a Madou Art technique. Upon her release, Exta took the appearance of a cat before possessing a homeless woman because her inner darkness. After the possession, Exta proceeds to eat two men that broke her disguise as a trash bag. After seeing a couple using vending machines, she decided to disguise as one. Just as she was about to lure a man towards her, her disguised is seen through by Raiga Saezima. She escaped the first encounter but was marked by crow's shuriken.
After that, when Raiga pursued her, she decided to take on the Makai knight and destroy him once and for all , taking the form of a excavator before turning into a giant spider-like form. She is killed by the Makai Knight with her essence congregates into a stone that Mayuri absorbs to seal the Horror.
She is a skilled shape shifter, however she have to hide her eyes more than often so that her disguise won't be seen through. Her actual form is like a spider-like creature.
In the series, Exta is the 2nd of the nine Horrors used as the foundation to seal Eyrith in the Ady Slate to be captured, though she is not the carrier of Eyrith's seed.