On the Events After Nichiren’s Passing
The Succession Issue

The “Go-yui-gon” {“Nichiren’s Last Will & Testament”), part of the authenticated “Shuso Gosenge Kiroku”, reads:
“The Honorable testament dictates: Of the Buddha; the standing statue of Shakya, must be placed beside [My] grave. Of the Sutra; My most essential writings, namely, the explanatory notes to the Hokkekyo, [Chu Hokekyo] are to be placed together, in the mausoleum. The six [equally ranked] disciples, at the time of their watch, must read these.
[literally: "Shakya standing statue grave beside must placed. My collection most essential writings namely explanatory notes Hokkekyou same basket place mausoleum. Six persons fragrant flower take turns read these."

It appears to declare that they are to be equally ranked at Minobusan Kuon-ji , like "6 petals of one Lotus." This is rather surprising, since Kounji is/was in Kai Province, which was Nikko's territory. The Jito; Hakiri Saburo, aka Hakiri Rokuro Sanenaga, Nambu Rokuro Sanenaga, or Nichien Nyudo, was Nikko's direct disciple. It seems like Nichiren would have left Nikko in charge there.
However, the "Rotating Chief Priest" concept is reinforced by a second authenticated document, one that is very clear. "Hakasho Mamorubeki Bancho no Koto" {"The Shift for Protecting His Mausoleum"} reads:
The Enactment: No rank is observed.
The Shift for Protecting His Grave:
The 1st month: Ben-Ajari
The 2nd month: Daikoku-Ajari
The 3rd month: Echizen-ko and Awaji-ko
The 4th month: Iyo-ko
The 5th month: Renge-Ajari
The 6th month: Echigo-ko and Shimotsuke-ko
The 7th month: Iga-ko and Chikuzen-ko
The 8th month: Izumi-ko and Jibu-ko
The 9th month: Byakuren-Ajari
The 10th month: Tajima-ko and Kyo-ko
The 11th month: Sado-ko
The 12th month: Tanba-ko and Jakunichi-bo
The order of the shift above must be kept and served without negligence.
The 1st month of the 6th year of Koan

("Hakasho Mamorubeki Bancho no Koto" Complete Works of Successive High Priests of Nichiren Shoshu, Vol. I, pp. 86-87)
====================================================================================================== My source for this is "Koshi-e, February 8th, 2004. [Nichiren Sgoshu] Myosenji Temple, [by] Rev. Shoshin Kawabe. Kawabe writes:
“In the 1th month of the next year, Nikko Shonin and disciples of the Daishonin enacted “The Shift for Protecting His Mausoleum.” … This enactment was ordained based on the Daishonin’s last will. On the back of this document are the signatures of four of the Six Major Disciples: Nissho, Nichoro, Nikko and Nichiji. Due to circumstances, Niko and Nitcho could not attend both the Daishonin’s funeral and the conference in Kuon-ji Temple.”
The rather dubious “Minobu-san Fuzoku Sho” aka “Ikegami-sojo-sho” reads:
“I transfer the Venerable Shakyamuni’s teachings of fifty years to Byakuren Ajari Nikko. He is to be the Head Priest of Minobu-san Kuonji Temple. Those priests and lay believers who refuse to accept this are slanderers of the Dharma.”
The thirteenth day of the tenth month on the fifth year of Koan at Ikegami
Musashi Province
Two documents, the “Shuso Gosenge Kiroku/Go-yui-gon” and “The Shift for Protecting His Mausoleum,” both accepted as authentic by Nichiren Shoshu, both authored by Nikko, indicate that Nichiren’s Elder Disciples were to basically take turns as Chief Priest at Kuon-ji. Meanwhile, a document of dubious origins; the “Ikegami Sojo”, names Nikko as Chief Abbot of Minobu. Which of these should one trust?
See Also:
Distribution of the Mementos?
The Distribution of the Mementoes/Responses to Hirahara
The Ikegami Transfer Document? Part One