Kuon jitsujo (久遠実成)

"Kuon jitsujo" is the thought in the teachings of Hoke-kyo Sutra (the Lotus Sutra) according to which Buddha was not enlightened at the age of thirty-five but was coming from the eternal past as Buddha (the enlightened one) by Rinne Tensho (the belief that all things are in flux through the endless circle of birth, death, and rebirth, or the circle of transmigration). Kuon jitsujo is also called "kuon jojitsu" and "kujo shogaku."
Kuon' is a word for 'eternity' in kango (words of Chinese origin) and means 'perpetual time.'

It is written as follows in the Hoke-kyo Sutra (Lotus Sutra), Nyorai Juryo-hon (Duration of the Life of the Tathagata), Chapter 16.

"All believe that the present Shakyamuni Buddha, after leaving the palace of the Shakyas, seated himself in the place of practice not far from the city of Gaya and there attained annuttara-samyak-sambodhi (perfect enlightenment). But good men, it has been immeasurable, boundless hundreds, thousands, ten thousands, millions of nayutas of kalpas since I in fact attained Buddhahood;" and the following continues. "Suppose a person were to take five hundred, a thousand, ten thousand, a million nayuta asamkhya thousand-million-fold worlds and grind them to dust."
"Then, moving eastward, each time he passes five hundred, a thousand, ten thousand, a million nayuta asamkhya worlds he drops a particle of dust. "
"He continues eastward in this way until he has finished dropping all the particles."
"Good men, what is your opinion?"
The above question was addressed to Miroku Bosatsu (Buddha of the Future, Bodhisattva of the Present).

The same story also appears in Kejoyuhon, Chapter 7.

"Suppose, for example, that someone took all the earth particles in the thousand-million-fold world and ground them up to make ink powder, and as he passed through the thousand lands of the east, he dropped one grain of the ink powder." "Such a grain is no bigger in size than a speck of dust." As described above, this chapter contains a similar story; this story is called sanzen-jin-tengo (an immensely long period of time). In response, the 'five hundred, a thousand, ten thousand, a million nayuta asamkhya worlds' according to Juryo-hon (Honmon, or the last fourteen chapters of the Lotus Sutra) came to be called "gohyaku (oku) jin-tengo" (fifty billion Dust Particle Kalpas) to suggest that it was infinitely farther than the "sanzen jin-tengo" (three thousand Dust Particle Kalpas) according to Kejoyuhon (Shakumon, or the first fourteen chapters of the Lotus Sutra).

It seems that the "gohyaku jin-tengo" was quoted only as a metaphor in the Lotus Sutra; however, Nichiren (founder of the Nichiren sect) gave the meaning of kaigon-ken-non (discarding the assumption that Shakyamuni attained enlightenment for the first time in India and revealing that he originally gained enlightenment in the immensely distant past) to the word "gohyaku jin-tengo" by saying things like "for as long as gohyaku jin-tengo, this land has been ruled by Buddha;" thus it came to be interpreted as the time of actual enlightenment of Buddha. After Nichiren's death, however, some of his disciples argued that Buddha was honbutsu (principal object of worship) while some others argued that Nichiren was honbutsu, due to split among disciples, etc. For example, Komon school, which preached goju sotai (five successive levels of comparison set forth by Nichiren) and montei hichin (literally, "hidden in the depths of the text"), combined the term "gohyaku jin-tengo" with the words," I have followed Bodhisattva's Path and attained a life which has not ended yet," also from Juryo-hon, and treated the same as referring to the time of "yushiyushu" (literally, "every beginning has an end") as realized by Buddha. Accordingly, Komon school created the word "kuon ganjo" (literally, "kuon" means "remote past" and "ganjo" means "beginning/foundation;" refers to eternity with no beginning or end, like reincarnation), and regarded Nichiren as honbutsu.