In Kenchō 5 (1253), having moved from Awa Province to Kamakura, Saint Nichiren built a hermitage in this Matsubagayatsu valley and began preaching the Lotus Sutra. In Bun'ō 1 (1260), in reaction to his submission of the Risshō Ankoku Ron to regent Hōjō Tokiyori, the 'Matsubagayatsu Persecution' (the burning of his hermitage) took place here in the eighth month — Nichiren escaped miraculously. More than seventy years after his death, in Enbun 2 (1357), the priest Nichiei, son of Prince Moriyoshi, formally founded Myōhōji on the site of the former hermitage. The 'Old Site of Nichiei's Matsubagayatsu Hermitage' remains in the precinct, preserving this place as sacred ground from the earliest days of Nichiren's Kamakura preaching.

Prince Moriyoshi, son of Emperor Go-Daigo and Seii Taishōgun under the Kenmu Restoration, was confined in Kamakura after a falling-out with Ashikaga Takauji and killed amid the chaos of the Nakasendai Disturbance in Kenmu 2 (1335) on the orders of Ashikaga Tadayoshi. His son by Lady Minami (daughter of Fujiwara no Yasutō), the priest Nichiei, later took Buddhist orders and, drawn to the legacy of Saint Nichiren, in Enbun 2 (1357) built halls on the site of Nichiren's Matsubagayatsu hermitage to memorialize his father and formally founded Myōhōji. Prince Moriyoshi's tomb is enshrined at the summit on the right side of the precinct, while the tombs of his mother Lady Minami and Nichiei himself stand together at the summit on the left — silent witnesses to the tragedy of father and son. The mountain name 'Ryōgonzan' derives from Nichiei's childhood name Ryōgonmaru.