The play might be Kamakura sandaiki (or an adaptation of the same tale, such as Ômi genji senjin yakata), a jidaimono originally written for the ningyô jôruri (puppet theater). It chronicles events linked with the fall of Osaka Castle in 1615, but set back in the Kamakura period (1185-1333) to avoid the Tokugawa shogunate's censorship of staging recent historical events involving the ruling samurai class.
Ômi Genji senjin yakata (The castle vanguard of Ômi Genji: 近江源氏先陣館) was written by Chikamatsu Hanji, Miyoshi Shôraku, and others, premiering as a nine-act puppet play (ningyô jôruri: 人形淨瑠璃) at the Takemoto-za, Osaka, in 1769; the first kabuki production took place the following year at the Naka no Shibai, Osaka. Originally in twelve acts, it dramatizes the battle over Osaka castle in 1615 when Tokugawa Ieyasu defeated Toyotomi Hideyori. Due to censorship against depicting events about the Tokugawa shogunate, the playwrights used as their "world" (sekai) the Kamakura period (1185-1333), also changing historical names, as with Sasaki Takatsuna (the historical Sanada Yukimura).
The main plot involves a young Genji warrior named Sakamoto Miuranosuke Yoshimura who is engaged to Princess Toki-hime of the enemy Heike clan. He is mortally wounded at the battle for Sakamoto Castle, but manages to visit his ailing mother, Nagato, one last time. Given her love for Miuranosuke, Toki-hime is sympathetic to the Genji cause and is ministering to Nagato. When summoned back by her father, the Heike general Hôjô Tokimasa (the historical shogun Tokugawa Ieyasu), Toki-hime initially refuses. A series of complications ensue, leading to Nagato's suicide so that Toki-hime can pretend she killed Nagato in the service of Tokimasa. Miuranosuke then urges Toki-hime to kill her father and then herself, whereupon he returns to battle to die. Then the Genji general Sasaki Takatsuna, in disguise and pretending to be an ally of the Heike (he is plotting to kill his younger brother, Saskai Moritsuna, who is the historical Sanada Nobuyori), informs Toki-hime that he will spare her from following Miuranosuke's wishes by assassinating Tokimasa himself. Torn between loyalty to her father and Miuranosuke, Toki-hime substitutes herself, tricking Takatsuna into beheading her. When he realizes his mistake, he, too, takes his own life.
This play is known for a famous kubi jikken ("neck [head] inspection": 首実検) scene, when the general Tokimasa comes to believe prematurely that Takatsuna is dead. He orders Moritsuna to examine what is purportedly Takatsuna's severed head, whereupon Koshirô (Takatsuna's son) — who has been hiding and not seen the head — commits ritual suicide (seppuku: 切腹) in a gesture of filial piety. After Moritsuna examines the face and is shocked to see that it is not his brother's, he remains silent, concealing Takatsuna's plot out of compassion for his nephew Koshirô's sacrifice. Through his pretense, Moritsuna betrays Tokimasa, leaving himself only one option — to die honorably in battle.
The dying Miuranosuke is shown in a dramatic pose (mie) before returning to battle at Sasaki Castle. He would have been accompanied in this scene by Takatsuna striking a similar mie. The armor (yoroi) is rendered in impressive detail, evidence of the skills of the celebrated block cutter Kasuke, whose seal is near the publishers' marks at the lower right.
Note: A rare find! This design appears to be unrecorded, as is the performance, which was likely from a middle theater (chû-shibai).
References: NKE, p. 264