Yukimura had an impregnable fortress at Osaka Castle. In 1614, the Tokugawa army unsuccessfully laid seige to it. Ieyasu then proposed a reconcilation, conditional upon the destruction of the outer moat of Osaka castle. His envoys destroyed not only the outer, but also the inner, moat, leaving the castle defenseless. On May 6, 1615, Ieyasu attacked again. Though Yukimura's army was outnumbered, it withstood the attack, and, the next day, Yukimura and a few soldiers invaded Ieyasu's camp directly. Legend has it that Yukimura wounded Ieyasu in the kidney, but was killed by a Tokugawa samurai who came upon him after the attack. The sources I have consulted believe that this print is intended to portray Sanada making his way to Ieyasu's camp before this incident.
This print is one of a series of thirteen, commissioned by the publisher Masadaya, the only commission Yoshitoshi received in 1872, the depth of his financial troubles and depression. The series is notable for early indications of Yoshitoshi's mature style. The posture, personality and composition all point in the direction Yoshitoshi would later explore so completely.