An Imperial Envoy has been ordered to visit Tsumori Bay in the Settsu Province (today Osaka prefecture) in order to purchase jewels coming from Korea and China. Upon reaching Tsumori Bay together with his Retainers, he meets a strange Boy who appears to be Chinese though he speaks Japanese. Surprised, the Envoy asks him about the jewel he is carrying on a silver plate. The Boy explains that the jewel belonged to a Dragon Princess and that it has the power to grant any wish. He wants to offer the jewel to the Emperor. The Boy then reveals to be the manifestation of Amano-sagume, a goddess that is said to have reached the Osaka Bay rowing a stone boat. Soon after, he flies into the sky and disappears. The Spirit of a Fish appears and relates the legend of Amano-sagume, then dances in celebration. Soon after, a Dragon God, protector of the Stone Boat transporting the gods across the skies, appears from the sea. Invoking the Eight Dragon Kings, he moors the Stone Boat at Tsumori Bay and unloads a wealth of jewels and treasures. Then, he bestows blessings on the land before disappearing.
Iwafune is an auspicious play centering on the theme of the Dragon God presenting the Emperor with jewels and bestowing blessings on the land. The “Stone Boat” giving the title to the play is the vessel on which gods travel across the sky. The Manyōshū anthology contains a poem attributed to Amano-sagume, which is thought to have inspired the play.
Since ancient times the port of Tsumori (present-day Sumiyoshi, close to Osaka) has played an important role in the cultural and commercial exchange between Japan and the continent, and was frequented by people from different cultural backgrounds.
The goddess Amano-sagume appears in the Kojiki and in the Nihon Shoki chronicles of myths. While today the main character in the first half appears as a boy, it is thought that anciently it was a female character. Old performances also featured a stage property representing the stone boat in the second half, while today it is left to the imagination of the audience.
Due to its congratulatory nature, performances in which only the second half is staged are frequent.