Having been ousted by his uncle, Prince Ōtomo, the Emperor (Emperor Kiyomihara in the play, though historically this was Prince Ōama, later Emperor Temmu)(ko-kata) flees to Mount Yoshino together with his retainer (waki) and his palanquin bearers (waki-tsure). Meanwhile, an elderly couple (shite and tsure of act one) living in Mt. Yoshino are sailing on a riverboat and admiring the sight of the purple clouds. They hurry home, as they interpret this as a sign of a nobleman's visit. Upon arrival, they find the Emperor waiting for them. The old couple is asked to prepare a meal for the Emperor, and they offer him some parsley and Kuzu-fish (sweetfish).
Having eaten half of the fish, the Emperor gives the remaining food to the old man. The old man notes that the Kuzu-fish still looks alive, and so he will release it back into the river. He recounts a legend about Empress Jingū who caught a Kuzu-fish, which turned out to be a good omen for her victory over Silla. He adds that if the Emperor is destined to return to the capital, the Kuzu-fish would come back to life. The old man then releases the fish into the river, and lo and behold, it starts swimming around the rocks, alive and well. However, their joy at the good omen is short-lived, as the Emperor's pursuers (ai) catch up with him. The old man hides the Emperor under his boat and confronts the pursuers.
The pursuers make an attempt to search the boat, but burning with indignation, the old man threatens to summon his allies and relatives from around the mountain. The old man's ferocity pushes the pursuers away. The elderly couple weep as the Emperor expresses his gratitude for their loyalty, saying that he would never forget the favour. Night falls and the area falls quiet. Suddenly, beautiful music echoes all around, the old man and woman vanish from sight, and a heavenly maiden (tsure of act two) appears in their place. As she dances, Zaō Gongen (shite of act two) also appears. Zaō Gongen blesses the whole land with prosperity and celebrates the arrival of the reign of Emperor Temmu (Emperor Kiyomihara).
"Kuzu" is set against the backdrop of the Jinshin Rebellion, a struggle for the succession to the throne between Emperor Tenji's son, Prince Ōtomo, and Emperor Tenji's younger brother, Prince Ōama (here referred to as Emperor Kiyomihara, later Emperor Temmu). In the Noh play, however, it is Ōtomo that is regarded as the uncle of Ōama, and not the other way around. There are many other elements that differ from historical fact. The collection of tales "Uji Shūi Monogatari" contains a story in which the Emperor divines his fate from some chestnuts he eats, and hides under a boat to escape from his pursuers.
The scene where the sweetfish left over from the Emperor's meal is released into the river is called "Ayu-no-dan", and is one of the highlights of the play.
In this short scene, the overwhelming suspense over the uncertainty of a good or bad omen quickly transforms into a feeling of relief and excitement. The old man is portrayed as a mystical being who has the ability to sense omens and divine one's fate, but also as a man of extreme devotion who hides the Emperor under his boat and boldly overpowers his pursuers through sheer wit. In ancient times, the mountain people living in the upper reaches of the Yoshino River were called Kuzu. They are known to have been some of the first allies of the Yamato clan. It is believed that prior to the conflict with Prince Ōtomo, Emperor Kiyomihara became a Buddhist monk and lived in seclusion in Mount Yoshino where he interacted with the Kuzu people.
In the latter half of the play, the bright and buoyant musical accompaniment emphasises the sacred nature of Mount Yoshino. The heavenly maiden performs a dance, creating an atmosphere of beauty and elegance. The story of the heavenly maiden dancing before the Emperor at Mt. Yoshino is handed down as the origin of the court dance "Gosetsu-no-Mai". Zaō Gongen, who appears at the end of the play, is the Buddha of the Shugendō sect of Buddhism and the main deity of Kinpusen Temple in Yoshino. Just as the play's libretto reads "One foot in the air...", he is often depicted standing firmly on his left leg while raising his right foot and hand. Zaō Gongen's performance is extremely dynamic, as if soaring between heaven and earth.