Nichiren declares that the sutras themselves were his SOLE teacher

"Wondering how to resolve this dilemma, I made a vow. I decided that I would not heed the claims of these eight or ten schools, but would do as the Great Teacher T’ien-t’ai did and let the sutras themselves be my sole teacher, in this way determining which of the various teachings of the Buddha’s lifetime are superior and which are inferior. With this in mind, I began to read through all the sutras.

In a scripture called the Nirvana Sutra, the Buddha says, “Rely on the Law and not upon persons.” Relying on the Law here means relying on the various sutras. Not relying upon persons means not relying on persons other than the Buddha, such as the bodhisattvas Universal Worthy and Manjushri or the various Buddhist teachers I have enumerated earlier.” (Repaying Debts of Gratitude)