A tale of family tragedy in a time of war, where brothers are forced onto opposing sides of a conflict. The younger brother sacrifices his own child to further his cause, while the elder brother, moved by his nephew's courage and his brother's fierce determination, makes a life-or-death decision.

At Sasaki Moritsuna's camp on the shores of Lake Biwa, his brother Takatsuna's young son Koshirō is being held prisoner. The regent Tokimasa orders Moritsuna to perform a head inspection to verify whether a severed head belongs to Takatsuna.

In truth, Koshirō has allowed himself to be captured as part of his father Takatsuna's strategy — the boy is prepared to cut open his own belly so that the false head will be accepted as genuine. Moritsuna, deeply moved by his young nephew's bravery, declares the false head to be authentic during the inspection.

Moritsuna summons Kagaribi, who has been hiding nearby, and allows her to see her dying son one last time. Moritsuna confesses that he lied because he was moved by his brother's and nephew's extraordinary resolve. As Moritsuna praises the boy, Koshirō breathes his last.

When Moritsuna prepares to take responsibility by cutting his own belly, Wada no Hyōe appears and shoots through the armor chest, killing the spy Hangai Jūrō who had been hiding inside. Wada no Hyōe tells Moritsuna to honor his obligation when Takatsuna raises his army, then seizes the white banner of the Genji clan and departs.

The scene in which Moritsuna verifies the false head is the greatest highlight of this play. Looking at the counterfeit head, he realizes why his nephew cried out "Father!" and disemboweled himself — it was all part of his brother's strategy. Determined not to let the boy's death be in vain, he resolves to sacrifice himself. All of this inner turmoil is conveyed without a single line of dialogue, through acting alone. This head inspection scene is said to be "the longest and most difficult of all head inspection scenes" in kabuki. Moritsuna's deeply human struggle between love for his family and loyalty to his lord is portrayed with quiet intensity.

Koshirō is an exceptionally demanding role for a child actor. He shows childlike vulnerability when begging his grandmother to spare his life, yet demonstrates remarkable wisdom and courage by willingly disemboweling himself for his father's sake, desperately watching to see whether his uncle will keep the secret. This heartbreaking bravery never fails to move the audience.