On the night of June 21, 1582, Akechi Mitsuhide (明智光秀, Akechi Mitsuhide) led roughly 13,000 soldiers to surround the Honnō-ji (本能寺, Honnō-ji) temple in Kyoto. Inside, Oda Nobunaga (織田信長, Oda Nobunaga) — the man who had brought Japan to the edge of unification — was lodging with only a small personal guard. When Mitsuhide's men announced themselves, Nobunaga reportedly said, "So it has come to this." He fought back with bow and arrow until a wound forced him to retreat to an inner room, where he committed seppuku (切腹, seppuku). He was 47 years old, two days from his 48th birthday. His page Mori Ranmaru (森蘭丸, Mori Ranmaru) died fighting beside him.

By June 22, Mitsuhide controlled Kyoto. His army also attacked Nijō Palace (二条御殿, Nijō Goten) that first night, where Nobunaga's son Nobutada (信忠, Nobutada) was staying; Nobutada too committed seppuku rather than surrender. With both father and heir dead, Mitsuhide moved quickly to consolidate his position. He petitioned the Imperial Court for recognition. He sent dispatches to daimyo (大名, daimyō) throughout the region, offering land and alliance. He visited temples and donated silver to the court and to six major Kyoto institutions — buying time, buying legitimacy, buying goodwill.

None of it worked. The alliances he needed did not materialize. Hosokawa Fujitaka (細川藤孝, Hosokawa Fujitaka), father of Mitsuhide's son-in-law, shaved his head in mourning for Nobunaga — a pointed, public refusal. His son Tadaoki (忠興, Tadaoki) did the same. Tsutsui Junkei (筒井順慶, Tsutsui Junkei), whom Mitsuhide had counted on, wavered and then defected to the other side. Each letter that came back without a pledge of support was another day added to a countdown Mitsuhide had not fully considered when he gave the order to march on Honnō-ji.

Why did Mitsuhide strike? The honest answer is that no one knows. More than fifty theories have been proposed in the centuries since: personal humiliation inflicted by Nobunaga in front of his peers; political ambition; loyalty to the Imperial Court or the remnants of the Ashikaga Shogunate (足利将軍家, Ashikaga Shōgunke); the so-called Shikoku Theory, which suggests Mitsuhide was protecting his ally Chōsokabe Motochika (長宗我部元親, Chōsokabe Motochika) from a planned invasion. No consensus has emerged. The motive died with him.

While Mitsuhide spent his days in Kyoto seeking recognition he could not obtain, the most consequential man of the moment was moving at extraordinary speed far to the west. Toyotomi Hideyoshi (豊臣秀吉, Toyotomi Hideyoshi) had been besieging Takamatsu Castle (高松城, Takamatsu-jō) in Bitchū Province (備中国, Bitchū no kuni) when a fast courier brought him news of Nobunaga's death. Hideyoshi made an immediate decision: say nothing. He kept Nobunaga's death hidden, used that secret leverage to force a quick ceasefire on favorable terms with the Mōri clan (毛利氏, Mōri-shi), and extracted a seppuku from the Takamatsu commander Shimizu Muneharu (清水宗治, Shimizu Muneharu) as part of the peace agreement. Then, on June 25, the Chūgoku Ōgaeshi (中国大返し, Chūgoku Ōgaeshi) — the Great Return from Chugoku — began.

What followed was one of the most celebrated forced marches in Japanese military history. Hideyoshi's army covered approximately 200 km in roughly seven days, sustaining a pace of up to 40 km per day. Logistics were pushed to the limit. By June 29, his forces had reached Amagasaki (尼崎, Amagasaki), at the edge of the Kyoto basin. The night before the final battle, Hideyoshi's generals sent agents into Mitsuhide's camp to set fires and spread confusion. Mitsuhide had controlled Kyoto for nearly two weeks. He had perhaps another twelve hours.

On July 2, 1582, the two armies met at the Battle of Yamazaki (山崎の戦い, Yamazaki no Tatakai), near the junction of the Yodo and Katsura rivers south of Kyoto. The terrain was decisive: Hideyoshi sent a detachment the night before to seize Mount Tennōzan (天王山, Tennōzan), which commanded the road to the capital. Mitsuhide had not. With Hideyoshi's force of approximately 20,000 against Mitsuhide's roughly 10,000 — and the high ground lost — the battle lasted about two hours. Mitsuhide's army routed.

He fled toward his home domain of Sakamoto (坂本, Sakamoto). Near the village of Ogurusu (小栗栖, Ogurusu) in Yamashiro Province (山城国, Yamashiro no kuni), a group of bandits — in a practice called ochimushagari (落武者狩り, ochimushagari), attacking fleeing samurai after a battle — intercepted his small party. Mitsuhide was wounded, possibly killed outright by a bamboo spear. The exact circumstances remain uncertain. His head was hidden in a bamboo grove by a loyal vassal.

Thirteen days. The phrase attached itself to him almost immediately, becoming the proverb 十三日天下 (Jūsan-nichi Tenka) — the Thirteen-Day Lord. The shorter form, 三日天下 (mikka tenka, the Three-Day Reign), entered everyday Japanese as an expression for any triumph that collapses almost as soon as it is achieved. Mitsuhide solved the right problem and failed to think three moves ahead. The moment he struck at Nobunaga, he started a clock he could not stop.