Nuu functions as a loyal wolf servant to the Genma ruler Maoh King. He first appears during the assault by Maoh King's soldiers on Hito village, arriving to retrieve Non after she consents to bear the king's child in exchange for her village's protection. Transporting Non to the castle on his back, this act of assistance enables her subsequent impregnation by Maoh King.

Following the birth of twins Loof and Gin, Maoh King assigns Nuu to monitor and protect Gin, the twin perceived as more human who remains with their mother Non. After Non's banishment from her village for bearing Genma children, Nuu actively aids in raising Gin within their secluded cave dwelling. He provides consistent support alongside Non's parents, regularly delivering essential supplies.

As Gin enters adolescence, Nuu observes the traumatic awakening of his latent Genma powers triggered when Maoh King's consort Parome commands soldiers to execute Non. During this attack, Nuu suffers fatal wounds while defending Gin, who unleashes his abilities in reaction to his mother's death. Nuu's killing by resistance leader Dan ignites Gin's vengeful rampage against the assailants.

Throughout the narrative, Nuu balances complex loyalties, dutifully serving Maoh King while forging genuine protective bonds with Gin and Non. His role shifts from a passive agent of the Genma to an active guardian within the exiled family. Posthumously, his influence endures as Gin internalizes their connection, later contemplating Nuu's significance during his travels with Loof.