The tide turned twice at Dan-no-ura (壇ノ浦, Dan-no-ura) — first in favor of the Taira, then against them, then into legend.

The Genpei War (源平合戦, Genpei Gassen) had been burning for five years, since 1180, when rival branches of the imperial house recruited the Minamoto and Taira warrior clans to fight their dynastic quarrels. The Taira under their late patriarch Taira no Kiyomori (平清盛, Taira no Kiyomori) had dominated the imperial court for a generation — Kiyomori once powerful enough to exile retired emperors and place a three-year-old grandson on the throne. That three-year-old was now Emperor Antoku (安徳天皇, Emperor Antoku), age seven, sailing in the Taira fleet through the narrow straits between Honshu and Kyushu with the Three Imperial Regalia and the last fighting strength of his clan.

The Kanmon Straits (関門海峡, Kanmon Kaikyō) are treacherous water. The tidal currents reverse with the hours and run fast between the two islands, and the Taira commanders knew them better than their opponents. On the morning of April 25, 1185, they used the morning ebb current to launch a three-pronged assault on the Minamoto fleet under Minamoto no Yoshitsune (源義経, Minamoto no Yoshitsune). The attack was aggressive and it worked — for a while.

As the afternoon came on, the tide reversed. The Taira ships found themselves fighting into the current while the Minamoto fleet found it behind them. And then the betrayal came.

Taguchi Shigeyoshi (田口重能, Taguchi Shigeyoshi) was a Taira commander whose son had been taken hostage by the Minamoto. Midway through the battle, he defected — swinging his squadron against the Taira rear and, in doing so, pointing out to Yoshitsune exactly which vessel carried the child-emperor and the regalia.

Yoshitsune had already shown he was willing to win by any means. Earlier in the day he had ordered his archers to target not Taira warriors but the helmsmen and oarsmen of the enemy ships — the men who directed and propelled the vessels. It was, by the standards of the era, deeply dishonorable. Warriors fought warriors. You did not shoot the rowers. The Taira commanders shouted their outrage across the water. Their ships began to lose steerage and drift. The outrage did not help.

With the fleet dissolving and capture minutes away, Taira no Tokiko (平時子, Taira no Tokiko) — known as Nii-dono (二位殿, Nii-dono), the Nun of the Second Rank, approximately sixty years old, widow of Kiyomori, grandmother of the boy-emperor — gathered Antoku in her arms. She is recorded in the 平家物語 (Heike Monogatari, Heike Monogatari) — the great literary chronicle of the war, compiled within decades of the battle — as telling him: 'The capital lies beneath the waves.' It was not comfort. It was the offer of another world, one below the sea where enemies could not follow.

She stepped off the ship.

The Kusanagi sword (草薙剣, Kusanagi no Tsurugi) — one of the Three Imperial Regalia, the legendary blade said to have been given by the goddess Amaterasu to the hero Yamato Takeru, housed since ancient times at Atsuta Shrine in Nagoya — went with her to the bottom. It has never been recovered. The version now at Atsuta Shrine is acknowledged by the shrine itself to be a replacement. The original remains somewhere in the Kanmon Straits.

The senior Taira commander, Taira no Munemori (平宗盛, Taira no Munemori), was pulled from the water alive. He begged for his life. He was taken to Kyoto and beheaded. Most other Taira nobles drowned or were killed. The phrase 平家の如く (Heike no gotoku, Heike no gotoku) — 'as if the Taira had fallen' — entered the Japanese language as an idiom for total, irreversible collapse.

Minamoto no Yoritomo (源頼朝, Minamoto no Yoritomo), who was not present at the battle and had in fact spent much of the war managing politics from Kamakura while his brilliant younger brother Yoshitsune did the fighting, moved quickly to consolidate the victory. By late 1185 he had extracted from the imperial court the right to appoint military stewards and tax collectors in every province — effective control of the country. In 1192 he was named 征夷大将軍 (Sei-i Taishōgun, Sei-i Taishōgun) — shogun.

For the next 677 years, that title — or its institutional successors — held real power in Japan. The emperor was honored, worshipped, and set aside. The samurai governed. All of it flows from the afternoon of April 25, 1185, in the churning water of the Kanmon Straits.

The heike-gani crabs (平家蟹, heike-gani) still live in those waters. Their shells carry markings that resemble a human face — a tormented, staring face. Fishermen have released them back into the sea for centuries, unwilling to eat what might be the spirits of the drowned Taira warriors. Science has a different explanation. Both can be true at once.