Since Śākyamuni Buddha is eternal and all other Buddhas in the universe are His manifestations, then those great bodhisattvas who were taught by manifested Buddhas and who are from other worlds are all disciples of Lord Śākyamuni Buddha. If the “Life Span of the Buddha” chapter had not been expounded, it would be like the sky without the sun and moon, a country without a king, mountains and rivers without gems, or a man without a soul.

Kaimoku-shō, Open Your Eyes to the Lotus Teaching, Writings of Nichiren Shōnin, Doctrine 2, Page 75