He had handed his brother the keys to Japan, and his brother had sent killers in return.

At the Battle of 壇ノ浦 (Dan-no-ura) on April 25, 1185, Minamoto no Yoshitsune (源義経, Minamoto no Yoshitsune) commanded the 源氏 (Genji) naval assault in the straits near modern Shimonoseki (下関, Shimonoseki). The engagement ended the five-year 源平合戦 (Genpei Gassen) between the Minamoto and Taira clans. Yoshitsune's decisive tactical move — ordering his archers to target the Taira oarsmen rather than the warriors, stripping the 平家 (Heike) fleet of mobility — was considered dishonorably pragmatic by some accounts, and devastatingly brilliant by all of them. The child Emperor 安徳 (Antoku), eight years old, was drowned by his grandmother in the straits rather than allow his capture. The sacred imperial sword 草薙剣 (Kusanagi no Tsurugi) was lost to the sea. The 平家 (Heike) were finished.

Yoshitsune was approximately twenty-six years old. He had given his brother Minamoto no Yoritomo (源頼朝, Minamoto no Yoritomo) the keys to Japan.

Yoritomo's answer was to block him from entering 鎌倉 (Kamakura).

The falling-out had been building since the war. Yoshitsune had accepted court titles from the imperial court in 京都 (Kyōto) without Yoritomo's permission, operating with an independence that alarmed his brother. Yoritomo was building the 幕府 (bakufu) — the warrior government that would become Japan's first shogunate — and in that project, any rival power base, even his own brother's, was a structural threat. Yoshitsune's battlefield reputation — celebrated in the capital, beloved by commoners, spoken of in the same breath as the great warriors of legend — made him precisely the figure Yoritomo could not afford nearby.

On June 23, 1185, while waiting outside 鎌倉 (Kamakura) and forbidden to enter, Yoshitsune composed the 腰越状 (Koshigoe-jō): a handwritten petition to his brother listing his loyal service through the war, denying any ambition against Yoritomo's authority, and begging simply for an audience. The letter still exists. Yoritomo never replied.

In the autumn of 1185, Yoritomo sent men to Yoshitsune's 堀川 (Horikawa) mansion in 京都 (Kyōto) with orders to kill him. Yoshitsune escaped. He obtained an authorization from Cloistered Emperor 後白河 (Go-Shirakawa) to take up arms against Yoritomo — a dramatic gesture rendered meaningless by the fact that he had no army left to lead.

The 吾妻鏡 (Azuma Kagami) — the official chronicle of the 鎌倉幕府 (Kamakura Bakufu), written by the scribes of the very institution built on Yoshitsune's victories — records the aftermath with almost cruel precision. Around December 3, 1185, the chronicle notes Yoshitsune south of 京都 (Kyōto) with four retainers remaining: Izu Uemon-no-jo (伊豆右衛門尉, Izu Uemon-no-jō), Yataro Hori (堀弥太郎, Yatarō Hori), the warrior-monk 武蔵坊弁慶 (Musashibō Benkei), and one other. The December 3 entry notes specifically: Benkei squired. The December 6 entry names all four — one of the earliest historical confirmations that Benkei, a figure of enormous legend, had been a real person.

Benkei's history was already remarkable. A monk of enormous physical size, he had reportedly challenged every swordsman he could find on the bridge at 五条 (Gojō) in 京都 (Kyōto). Yoshitsune, then barely into adulthood, crossed that bridge and defeated him. Benkei swore lifelong loyalty on the spot. By 1185, that oath had been tested through the entire span of the 源平合戦 (Genpei Gassen) — and it was still holding, holding now when holding offered nothing in return but the road going north.

The four men traveled in disguise — dressed as 山伏 (yamabushi), mountain ascetic priests collecting donations to rebuild 東大寺 (Tōdaiji) temple in Nara, a cover story Benkei improvised at roadblocks when suspicious guards questioned the group. At one checkpoint, when an official grew dangerously inquisitive, Benkei publicly berated and struck his own lord for slowing the group's progress. A man being beaten in public by his own servant could not possibly be the great Yoshitsune. The ruse worked. They passed.

They reached 平泉 (Hiraizumi) in Mutsu Province (陸奥国, Mutsu no Kuni), far to the north, under the protection of Fujiwara no Hidehira (藤原秀衡, Fujiwara no Hidehira). For roughly two years they had sanctuary. Then Hidehira died in October 1187, and his son Yasuhira (泰衡, Yasuhira), under relentless pressure from Yoritomo, made his choice.

On June 15, 1189, Yasuhira sent five hundred soldiers to surround Yoshitsune's residence at 衣川館 (Koromogawa no Tachi). Yoshitsune killed his wife and daughter, then ended his own life. He was approximately thirty years old. At the gate bridge, 武蔵坊弁慶 (Musashibō Benkei) held the crossing against Yasuhira's army. His body was found standing afterward, riddled with arrows — the soldiers reportedly hesitated to approach, unsure whether he was still alive. This became known as 弁慶の立ち往生 (Benkei no Tachi Ōjō): Benkei's Standing Death.

The particular irony: the 吾妻鏡 (Azuma Kagami), the shogunate's own official record, is the source that preserves Yoshitsune's story most vividly. History was written by his enemy's scribes. They are the reason we still know Benkei's name.