Niko (1253-1314) was the son of a samurai from Mobara, Kazusa. He was a novice priest at Mt. Hiei at the time his father met Nichiren Shonin in 1265. His father was so impressed that he had Niko brought back from Mt. Hiei in order to become a disciple of Nichiren Shonin. Niko taught the Lotus Sutra in his home town Mobara, but when he found out about Nichiren Shonin's exile he joined him on Sado Island. For this reason, he is known as the Sado Master.
After Nichiren Shonin's death, Niko founded the Myokoji Temple in Mobara. In 1285, he left Mobara to help Nikko at Mount Minobu. Unfortunately, he and Nikko were not able to reconcile their differences regarding the conduct of Lord Hakii, and so Nikko left in 1288. Niko was then solely in charge of Mount Minobu, but he continued to make trips back to Mobara. For this reason, Niko is considered the founder of two lineages: the Mobara Lineage and the Minobu Lineage.
Niko left his disciple Nisshin in charge of Mount Minobu, and his disciple Nisshu in charge of the Myokoji Temple in Mobara. The Myokoji Temple is now known as Sogenji Temple.