Stories of the Japanese 00525 [Early Kamakura Period] The Misunderstanding Between Brothers Seen in the Koshigoe Letter

The Koshigoe Letter was formally addressed to Oe no Hiromoto, but it was likely written with the expectation that Hiromoto would show it to Yoritomo himself. And it seems that this very document brilliantly illustrates the cause of the misunderstanding between Yoritomo and Yoshitsune.
First, while Yoshitsune appears to be apologizing profusely, he also takes pride in the fact that he destroyed the Taira clan, calling it something that 'should be highly praised,' and he does not admit to any fault of his own, stating that he has 'incurred imperial wrath without any sin.' Furthermore, parts such as 'without verifying the truth of the slander, you will not let me enter Kamakura' can also be seen as criticizing his older brother.
The reason Yoritomo is angry is, needless to say (though the Kusanagi sword incident is also a factor), that Yoshitsune accepted an official appointment without permission. The samurai band Yoritomo is trying to build is bound by strong master-servant relationships; if he were to allow appointments from the Retired Emperor Go-Shirakawa without his permission, there would be a risk that his retainers would side with the Imperial Court should Yoritomo and the Court come into conflict, which could lead to the collapse of the samurai band. To make matters worse, because Yoshitsune, who was in a position to strictly enforce Yoritomo's instructions, accepted an appointment without permission, many other retainers followed suit. Yoshitsune argues that there is no legitimacy to Yoritomo's anger, and he seems to completely fail to understand the cause of his brother's rage.
What is even worse is the point where he repeatedly appeals to their kinship, saying, 'The bond of blood-related kin will become empty.' Just as Yoritomo ordered Yoshitsune to lead his horse at the Tsurugaoka Wakamiya Shrine ridgepole-raising ceremony in the first year of Yowa (1181), he treats Yoshitsune not as a younger brother, but as an equal to his other retainers. This is necessary to avoid creating dissatisfaction among the retainers. Nevertheless, Yoshitsune does not understand this either and is asking to be treated as a younger brother.
Furthermore, by trying to elicit sympathy with irrelevant personal stories such as 'having become an orphan and held in my mother's bosom...', this likely only served to make Yoritomo even angrier.
This Koshigoe Letter is still preserved at Manpuku-ji Temple, but it is questioned whether it is the original written by Yoshitsune.
Now, for some reason, the Koshigoe Letter was often used for reading and writing practice during the Edo period. The popularity of Yoshitsune, the tragic hero, must have been particularly high during the Edo period. For this reason, after the Meiji era, many families discovered old Koshigoe Letters in their storehouses,
and people who thought, 'Could our family be of the Minamoto lineage?'
would take them to appraisers,
only to be disappointed when told, 'This was written by a child in the Edo period.'