Nichiren was first identified with the True Buddha by Nichigen (-1486) of Nishiyama Hommonji.  
  According to the Lotus Sutra, Sakyamuni Buddha, who was in the Stupa of Prabhutaratna Buddha,
  transmitted the Dharma to Visistacaritra Bodhisattva (Jogyo Bosatsu). Nikko held that Nichiren was the
  reincarnation of Jogyo Bosatsu. So did his disciple Nichizon (1265-1345), who founded Jogyo-in Temple
  in Kyoto, the temple being named after the Bodhisattva. But his disciple Hongaku Nichidai (1309-1369),
  went so far as to say that Nichiren himself entered the Stupa and received the Dharma directly from
  Sakyamuni Buddha. This misinterpretation of the Lotus Sutra finally culminated in the creation of the
  Nichiren-Is-True-Buddha theory by Nichigen.
 
  According to Nichigen, Sakyamunni Buddha saved people by the teaching of the Lotus Sutra. The Lotus
  Sutra was good only for the people living in the lifetime of Sakyamuni Buddha. We are not in the Age of
  Degeneration. The True Dharma, which is applicable to the people of this age, is not the Lotus Sutra but
  the word Myoho Renge Kyo. The word Myoho Renge Kyo is the seed of Buddhahood to be sown in the
  minds of people by the Original Buddha. The Nichiren Shoshu hold that only Nichiren sowed the seed of
  Buddhahood in the minds of people, and therefore, that Nichiren is the Original Buddha, the True
  Buddha.
 
  Those of the Nichiren Shoshu Sect never refer to Nichiren as "Nichiren Daibosatsu (Great Bodhisattva)"
  because they hold that Nichiren is the Buddha. We (Hokke Kai) worship Nichiren as the representative of
  the Samgha.
 
  In those days usurpation was frequent. The lower dominated the upper very often. The Emperor
  Gokomatsu was enthroned in 1382. His father, the Ex-Emperor Goenyu, died in 1393. The Gokomatsu’s
  mother died in 1406. It was believed to be ill-omened to hold and official Imperial Funeral twice during
  the regnal years of an emperor. There was a regulation that, if the Empress Dowager died after the Ex-
  Emperor during the regnal years of an emperor, a lady of the Imperial family should be installed as the
  mother-in-law of the emperor, and that the funeral of the natural mother of the emperor should be held
  unofficially. The Shogun Ashikaga Yoshimitsu violated this regulation. He appointed his wife, who was
  not a member of the Imperial family, as the mother-in-law of the Emperor Gokomatsu. Thus, Ashikaga
  Yoshimotsu held a ceremony of manhood for this second son Yoshitsugu. There ceremony was exactly the
  same as that performed when one is appointed Crown Prince. If Yoshimitsu had not died three days later,
  he would have obtained the title of Emperor or Ex-Emperor. He failed in his plot, but Nichigen succeeded
  in making Nichiren the True Buddha.