Minamoto no Yoshitsune, who annihilated the Taira clan in the Battle of Dan-no-ura, etched his name in history with his valor. However, his subsequent fate became complicated. The relationship between Yoshitsune and his brother, Minamoto no Yoritomo, deteriorated after Yoshitsune was appointed as the police/military official by Emperor Go-Shirakawa without Yoritomo's consent. According to the Azuma Kagami, this appointment was made without Yoritomo's approval, leading to Yoshitsune being denied entry into Kamakura and confined to Koshigoe. It is said that Yoshitsune wrote the Koshigoe Letter in defense, yet he was never forgiven, ultimately returning to Kyoto.
However, there are differing views regarding this sequence of events. Some suggest Yoshitsune was indeed appointed as the police/military official with Yoritomo's consent. Moreover, Yasuo Motoki, Emeritus Professor at Kyoto University, argues that if the relationship between Yoritomo and Yoshitsune had truly deteriorated, Yoritomo would not have allowed Yoshitsune to return to Kyoto but would have detained him immediately, suggesting that their relationship may not have been completely severed at that time.
Furthermore, Yoritomo later appointed Yoshitsune as the governor of Iyo, a high-ranking position, which was not a poor reward. However, issues arose as normally, one could not hold the positions of police/military official and governor simultaneously, but Yoshitsune did, enabled by Emperor Go-Shirakawa's influence. Yoshitsune's refusal to return to Kamakura, holding both positions, is considered to have decisively worsened his relationship with Yoritomo. Additionally, alternative theories suggest that despite being denied entry into Kamakura, Yoshitsune did meet Yoritomo there, where Yoritomo treated him coldly. Moreover, the narrative about the Koshigoe Letter in the Azuma Kagami may not be factual, and the content of the Koshigoe Letter itself could have been fabricated later to emphasize Yoritomo's cruelty.
