甲斐國
Nikkō was born at Kajikazawa in Koma District of Kai Province. His father, Oi-no Kitsuroku was from Totsumi province and later moved to Kai province while maintaining his Samurai career. He died when Nikkō was a child. Nikkō's mother was Myofuku Tsunashima () and was from what is now Shizuoka Prefecture. He was raised by his grandfather, Nyudo Yui. As a child, he entered the Tendai temple Shijuku-in, in Fujiwakabacho, Iwabuchi Ichirizuka. He took the acolyte name, "Hokibo" and received his education here, which as well as Tendai doctrine, included Chinese classics, Japanese literature, poetry, calligraphy, as well as other subjects.