Background
Masunobu (升信) was a student of Sadamasu (Kunimasu). He used the gô (art name) Ittôsai and was active for only a brief period, c. 1849-1853. His earlier art name was Kiyosada (清貞).
This diptych may be a mitate-e ("likening pictures" or analogues: 見立絵), used to denote portraits of actors who had not actually performed in the roles or with the other actors shown in the composition. The roles identified on the prints suggest the theatrical context is a Soga monogatari (Tale of the Soga: 曾我物語), a recounting of the revenge taken by the brothers Soga no Jûrô and Soga no Gorô against Kudô Suketsune, who murdered their father in 1193.).
References: OSP, no. 207