The idea held by some sects that Nichiren was the teacher of Shakyamuni in some remote past is nothing Nichiren ever claimed. That suggestion only obscures the Eternal Buddha and the teachings of the Lotus Sutra. It is also an attempt to elevate some Nichiren denominations by their claim that somehow they practice a True Buddhism that stands above the Lotus Sutra. It is only by discouraging their followers from actually studying the Lotus Sutra and by offering convoluted explanations that make no logical sense and fly in the face of Nichiren’s own teaching that these denominations seek to elevate their standing.
Lecture on the Lotus Sutra