Yuu Mononobe (物部 悠, Mononobe Yū) is the main protagonist in the Unlimited Fafnir series and the only male D in the world. He was formerly a Second Lieutenant at NIFL and captain of the Special Operations team Sleipnir. Upon his transfer to Midgard, he is assigned to Brynhildr Class as Student No 8 and later becomes a reserve member of the Counter-Dragon Squad. He is later revealed to be the Ninth Dragon.