"Thus it was revealed that Sakyamuni had long been the Buddha since the eternal past, and it became clear that various Buddhas in other worlds were all manifestations of Sakyamuni Buddha. In the pre-Lotus sutras, as well as the theological section of the Lotus Sutra, various Buddhas and Sakyamuni Buddha were on the same level, each practiced Buddhism on their own. Therefore, those who considered various Buddhas to be their main figures of worship did not worship Sakyamuni. Now, however, as Sakyamuni was proved to be the Eternal Buddha, those Buddhas on the lotus petals in the Flower Garland Sutra, or Buddhas in the Hodo, Hannya, or Great Sun Buddha sutras all became subordinates of Sakyamuni Buddha." -- Opening of the Eyes
"Again, if we consider the question of how long it has been since these various Buddhas attained the fruit of Buddhahood, then we will find that there are some who became Buddhas ten kalpas ago, others a hundred kalpas or a thousand kalpas ago. But in the case of ShakyamuniBuddha, the lord of teachings, it has already been a period of numberless major world system dust particle kalpas since he became a Buddha of perfect enlightenment and complete reward. The Thus Come One Mahāvairochana, the Thus Come One Amida, the Thus Come One Medicine Master, and all the other Buddhas of the ten directions are followers of Shakyamuni, the lord of teachings and our original teacher. He is like the moon in the sky that is reflected in ten thousand different bodies of water." -- Nichiren on why all other Buddhas are followers of Shakyamuni Buddha
"Reading this passage, we can see that the Lotus Sutra is none other than Shakyamuni Buddha himself. For persons who do not have faith in the Lotus Sutra, Shakyamuni Buddha has passed into extinction. But for those who put faith in the sutra, although Shakyamuni Buddha may seem to have passed into extinction, he is still present in the world.''
"In turbid water the moon does not abide; in a withered tree there are no birds. In the body of a woman without a mind [of faith] the Buddha does not abide. A woman who keeps the Hokekyo is like clear water: the moon of the Buddha Shakya takes up residence [there]. For example, although, when a woman is first pregnant, she is not aware of it in her own body, as the months gradually add up and the days pass, she first wonders if it is so and later thinks that it is certain. A woman of insight even knows whether it is a boy or a girl. The doctrine of the Hokekyo is also thus. When one believes Namu Myoho renge kyo in one's mind, the Buddha Shakya is conceived with the mind as His lodging. Though at first one does not know it, as the months gradually add up, the Buddha in one's mind appears and a joyful mind gradually emerges." -- Letter to Lord Matsuno's Wife