Kumagai-Jirō Naozane, who currently lives in Musashi Province, has killed Taira no Atsumori in the battle of Ichinotani in Tsu Province (now Suma District of Kobe City in Hyōgo Prefecture). He felt great remorse for killing Atsumori, became a Buddhist monk under the great priest Hōnen and changed his name to Rensei (waki).
Rensei travels back to Suma Beach to pray for the salvation of Atsumori's soul in the afterlife. Amid his prayers he suddenly hears the sound of a flute. He sees a group of grass cutters (shite and tsure of the first act), playing flutes on their way home. They tell Rensei about the songs of the woodcutters and the flutes of the grass cutters.
While most of the cutters continue on their way back home, one of them stays behind. After confessing to Rensei that he is, in fact, related to Atsumori, the man disappears into thin air.
A local man (ai), who happens to pass by, tells Rensei the story of Atsumori's death and the battle of Ichinotani. Rensei reveals that he is none other than Naozane, the man who killed Atsumori, and decides to spend the night on the beach in prayer for his soul's salvation.
At night, Atsumori's ghost (shite in the second act) appears, dressed in full armor. He expresses his gratitude to Rensei and narrates the story of his end.
Atsumori's ghost recalls the banquet with music in the evening before the battle, dances and reenacts the moment when he was slain by Naozane. In the end, he shows his appreciation for the memorial service again and, requesting further prayers from Rensei, vanishes from sight.
This is a "warrior" or "second-group" Noh play written by Zeami, based on "Atsumori's End" - the 9th chapter of the classic "Tale of the Heike". Its hero is Taira no Atsumori, a young general who was killed when he was just 16 years old. The "warrior" plays in Noh focus on the eternal torment of the ghosts of dead warriors who, after having been killed on the battlefield, have sunk to Shura-dō - the world of perpetual carnage. They usually ask for salvation and tell the story of their death in repentance.
The Noh play was contrived to reveal the character of Atsumori as he was depicted in "Tale of the Heike" - an elegant and noble youth who was fond of playing the flute.
In the first act of the play, the grass cutters don't have masks on and enter the stage bare-faced. The story about the cutters' flute, which states that the best flute is the one made of young leaves, hints at the refined qualities of the hero Atsumori.
In the second act, the ghost of Atsumori wears the mask of a noble lad in light makeup with blackened teeth. The highlight of this section is Atsumori's dance, describing his last banquet and subsequent death. He sings of the pitiful state of the Taira family and accompanies the description with fitting gestures.
As Atsumori dances he revives the memory of his last banquet night.
Atsumori sings about playing his flute at the banquet - a reference to the story about the cutters' flute in the first act.
In the end, he raises his blade against Rensei, but then he remembers that they are now both connected through Buddha's Law. Although they had first met as enemies, now through the power of Buddha, they will surely be reborn on the same lotus flower in paradise.