The “mutual possession of ten realms” doctrine is as difficult to maintain as it is to see fire in a rock and flowers in wood. However, it is not totally impossible because rocks spark when struck together and a tree blooms in spring. It is most difficult to believe that the realm of Buddhas is contained in the realm of men because it is just like saying that fire is in water or water is in fire. However, it is said that dragon fire comes out of water and dragon water comes out of fire. This is difficult to believe, but we cannot help but believe in it because of the evidence for this. You have come to believe that each of the eight realms is contained in the realm of men. Why can you not believe that the realm of Buddhas, too, is contained in it?

Ancient Chinese rulers, sages such as Yao and Shun, treated all people equally with compassion, proving the existence of the realm of Buddhas, at least a portion of it, within the realm of men. Never-Despising Bodhisattva, described in the 20th chapter on “Never-Despising Bodhisattva” of the Lotus Sūtra, pressed his hands together in respect and bowed to anyone he met because whenever the bodhisattva saw a man, he saw a Buddha in him. Born to the human world, Prince Siddhartha, young Śākyamuni, became the Buddha. These evidences should be enough to convince you to believe that the realm of Buddhas exists in the realm of men.

Kanjin Honzon-shō, A Treatise Revealing the Spiritual Contemplation and the Most Verable One, Writings of Nichiren Shōnin, Doctrine 2, Page 136-137