In 1185, having destroyed the Heike at Dannoura, Yoshitsune went down to Kamakura, where his brother Yoritomo waited, bringing the captured Taira no Munemori and his son.
But Yoritomo would not let Yoshitsune into Kamakura. The reasons were that Yoshitsune had accepted court rank without Yoritomo's permission, and that, through the slanders of Kajiwara Kagetoki, he was thought to have acted on his own again and again.
Yoshitsune was held at the post station of Koshigoe, just short of Kamakura. However many days he waited, no permission came from his brother. Yoshitsune sent a letter pouring out his heart to Oe no Hiromoto, Yoritomo's close adviser:
"I, Yoshitsune, as my brother's deputy, received the imperial command, destroyed the enemies of the court, and wiped away my father's shame. I thought I would be rewarded, but unexpectedly, through slander, my great deeds are ignored, I am blamed though I am innocent, and I can only weep.
"When I think of it, I lost my father as soon as I was born, and since I fled in my mother's arms to Uda in Yamato, I have not passed a single day, a single moment, in peace. I hid around the capital, made my home in far-off provinces, and served common folk and farmers.
"So, to strike the Heike, I did not spare my life; at times I whipped my horse over steep rocky mountains, at times I endured the wind and waves of the great sea, serving loyally with all my heart. I beg you to understand my feelings and arrange for my brother's forgiveness."
But this "Koshigoe Letter" could not move Yoritomo either. Yoshitsune was not allowed into Kamakura and went back to the capital with Munemori and his son. The decisive rift between the brothers began here.
Manpukuji in Koshigoe keeps a draft of the Koshigoe Letter said to have been written by Benkei.