Nikko (1246-1333) met Nichiren Shonin at Jissoji Temple in 1257. Nichiren Shonin was there doing research and writing the Rissho Ankoku-ron. Later, Nikko had many followers in the provinces of Suruga, Kai, and Izu. Nichiji, another of the Six Senior Disciples, was originally Nikko's disciple before becoming Nichiren Shonin's disciple. The Atsuwara Persection in 1279 was directed against Nikko's followers in Suruga Province. After Nichiren's death, the Six Senior Disciples and twelve junior priests were to take responsibility for tending his grave at Mount Minobu by using a rotation system (the Rinban). Of the twelve junior disciples, eight of them were the direct disciples of Nikko.
In September 1285 Nikko took up permanent residence on Mount Minobu because the rotation system had broken down. The other senior disciples lived further away and were having difficulties maintaining their communities in the face of government persecution. Nanbu Sanenaga, the Lord of Hakii, recognized Nikko as the chief priest of Kuonji Temple at Mount Minobu. Later in 1285, Niko came to Mount Minobu to assist Nikko. Unfortunately, relations between them all broke down soon afterwards due to Nikko's uncompromising nature and Niko's flexibility. The first problem occurred when Lord Hakii commissioned a statue of Shakyamuni Buddha for his home shrine. Nikko objected that the statue should be accompanied by the Four Great Bodhisattvas of the essential section of the Lotus Sutra if it was to represent the Eternal Shakyamuni Buddha. Niko, however, said that putting a copy of the Lotus Sutra in front of it would suffice. Another time, Lord Hakii made offerings at the Mishima Shrine. Nikko objected to this because according to the Rissho Ankoku-ron, the Shinto gods had abandoned the country because of it's slander of the Lotus Sutra. Niko, however, argued that the gods would surely protect the votary of the Lotus Sutra, and that Nichiren Shonin himself had prayed to them. Finally, he supposedly offered a horse and lumber to a stupa of the Pure Land sect at Mt. Fuji, but he argued that he had merely made a donation out of charity and did not know that it was going to support the Pure Land sect. In each case, Niko supported Lord Hakii while Nikko admonished him. In the end, Nikko no longer felt welcome and decided to leave for his mother's old home in Fuji, Ueno on December 5, 1288.
In 1290, the Lord of Ueno, Nanjo Tokimtsu, built the Taisekiji Temple at Oishigahara for Nikko. Nanjo Tokimitsu, the Lord of Ueno, was the uncle of Nikko's disciple Nichimoku.
In 1291, Nikko moved to the town of Omosu in Kitayama where he founded the Honmonji Temple in February 1298 with the help of Nitcho. He spent the rest of his life at this temple. His lineage is referred to as the Fuji Lineage.
Nikko appointed two sets of six senior disciples to take over for him after his passing. The first set consisted of: Nikke, Nichimoku, Nisshu, Nichizen, Nissen, and Nichijo. The second set consisted of: Nichidai, Nitcho, Nichido, Nichimyo, Nichigo, and Nichijo.