This letter was written at Minobu in the eleventh month of the third year of Kōan (1280) in response to a petition from the lay nun Nichigon. She is thought to have been either a relative of the lay priest Takahashi, a central figure among the believers in Fuji District of Suruga Province, or the mother of Nichigen, a priest of Jissō-ji temple in the same province who converted to Nichiren Daishonin’s teachings.

https://www.nichirenlibrary.org/en/wnd-1/Content/155?cmdf=reply+to+lay+nun+nichigon