This letter was written at Minobu in 1278 to Shijō Nakatsukasa Saburō Saemon, commonly called Shijō Kingo. Kingo was accomplished in both the practice of medicine and the martial arts. For nearly the entire first half of 1278, Nichiren Daishonin had suffered from debilitating and chronic diarrhea. Evidently Kingo had sent the Daishonin various medicines that had helped alleviate his illness.

In the fall of 1277 a virulent epidemic swept Japan, and Kingo’s lord became violently ill. Despite the lord’s deep-seated antagonism toward the Daishonin’s teachings, he turned to Kingo for help. Lord Ema was most grateful for Kingo’s ministrations and rewarded him with an estate three times larger than the one he already had. Yet the Daishonin warns Kingo to be constantly on guard and to take particularly great care to protect himself from attack while traveling.

https://www.nichirenlibrary.org/en/wnd-1/Content/128