Yūki Masanao served as a bushi during the Sengoku period. He is surmised to have served as the sixteenth head of the Yūki clan of Shimōsa Province.
Masanao was born as the eldest son and lineal heir of Yūki Masatomo, the fifteenth head of the Yūki.
According to the genealogical records of the Yūki family, Masanao is not indicated as a head of the clan, but his existence has been confirmed from documents issued during the period and he is considered to have been the head of the clan or at an equivalent level of status. Moreover, Yūki Shichirō is a name that was used by generations of lineal heirs of the clan.
Around this time, the Yūki clan was grappling with various problems, including the transfer of Takatomo (known as Oyama Takatomo) to become the adopted heir to the Oyama clan, and is regarded to have been a period of instability for the family. It is said that Masanao may have been caught-up in some type of dispute during this time.