Fermaus is the currently the Heaven's Blade Quantis Successor after the death of Delbone Quantis Myuura she now known as Fermaus Quantis Foa.
She is usually seen wearing a mask and is wholly clad in a robe and hood. Besides that, she also carries a leather bag. However, though her outfit completely hides her skin, it is noted that her skin is as black as coal and her facial features is missing a nose bridge and eyelids. Her mouth is torn and remains solidified.
A Glendan-born veteran who was acquainted with the first generation leader since a young age and knows Derek as well. She is in fact female and the granddaughter of Heaven's Blade wielder, Delbone. Her real name is Elsmau Foa, a genius psychokinesist who is also approved by Queen Alsheyra and Haia's guardian. She is able to discern a filth monster's scent and is resistant to pollution. In addition to her normal abilities, she can sense filth monsters as long as she goes outside the air filter without any other equipment. As a result, she has to pay the price of her body rotting away and is forced to wear a mask. Since she has also lost the function of her vocal cords, she is only able to communicate with psychokinesis through her nen-i terminal. Her age is unknown.
She states that humans may find a way to overcome the pollutant if they studied her body. Fermaus wanted to meet Layfon for a while but gave up on the idea because he wasn't planning on returning to Glendan. Fermaus notes that Haia is unable to defeat Layfon even if Layfon is exhausted or injured. Her psychokinesis pins are blue.
In the novel, after Haia disappears, she serves as the representative of the mercenary team. In vol.14, after receiving a skin graft surgery, she receives the Heaven's Blade informally from Delbone before her grandmother died, but later she was chosen by the Queen which makes her an official successor of that Blade.With Felli's help, Fermaus was able to save Glendan from its crisis. In vol.15, she officially receives the Heaven's Blade as Delbone's successor and builds a new network for the nen-i terminal. She regains her appearance as a female but her facial muscles is not established and is therefore, expressionless.Source:Wikipedia