Not a person but a white crow tengu spirit that Adarian captured[1] and imprisoned within the Book of the Malachai, she has existed since the dawn of the primals. As a Malachai unlocks his powers, incantations appear that will allow them to further hone their skills. Originally it belonged to the Malachai Adarian back when he was enslaved by Noir. The book was left behind when the Malachai escaped and was hidden from Noir by Seth, who later on at some point gave it to the current Malachai, Nick. It carries a number of secrets and not just magic.
In Instinct, Nick freed Nashira from the book after Livia slit his throat. In return she helped Aeron heal Nick.
Also in Instinct, Nick declares Nashira one of his Generals.