The Akazu no mon (Unopened) Gate at the Head Temple is located in front of the Kyakuden (Reception Hall). This gate is reserved for the head of state at the time of Kosenrufu.
This term signifies the condition in which all people throughout the world take faith in Nichiren Daishonin’s Buddhism, Nam-Myoho-Renge-Kyo of the Three Great Secret Laws.
The term originates in the Bodhisattva Medicine King (Yakuo bosatsu; twenty-third) chapter of the Lotus Sutra, which states:
In the fifth five-hundred year period after my [Shakyamuni’s] passing, the Law will be propagated throughout the world. (Hokekyo, p.539)
This passage indicates that in the Latter Day of the Law, two thousand years after Shakyamuni’s passing, the teachings of the Lotus Sutra will benefit all people in the entire world. Nichiren Daishonin states in the “Selection of Time:”
There should be no doubt that the great pure Law of the Lotus Sutra will be spread throughout Japan and the rest of the world. (Gosho, p.843)
Thus, Nichiren Daishonin, in his final will, encouraged all disciples and believers to endeavor in shakubuku and propagation efforts with the spirit of many in body, one in mind in order to accomplish kosen-rufu.
Reference: Basic Terminology of Nichiren Shoshu, p.71.