Wish-fulfilling gems are in fact the relics of Śākyamuni Buddha. They are given to a dragon king to crown his head, and Indra causes the gems to rain. How did the relics of the Buddha become wish-fulfilling gems? The merit of the Buddha gained by observing the precepts since immeasurable kalpa (aeons) in the past seeped into His flesh and bones and became gems to save all living beings. This is like the fangs of a dog that melt upon biting a tiger’s bone, or fish bones swallowed up by a cormorant. It is also like a string of a koto made of lion’s muscle; when it is played, the strings made of other animal muscles are all cut. The Buddha’s sermons are called the lion’s roars, and the Lotus Sūtra is the foremost of His sermons.

Shijō Kingo-dono Gohenji, Response to Lord Shijō Kingo, Writings of Nichiren Shōnin, Followers I, Volume 6, Page 118