Seijuro is a character that appears in For Honor's Singleplayer Campaign as well as the secondary antagonist of the Samurai Story.
One of the Daimyo and one of the greatest warriors in the Dawn Empire, when Apollyon assassinated the Emperor, it was Seijuro who stepped up, vowing to kill his competitors before coming after her. Apollyon recognized him as a wolf among the sheep and permitted this. When Ayu arrived at the palace with an army to overthrow his rule, Seijuro refused. After The Orochi snuck in and destroyed the gate controls, letting the army in, they confronted Seijuro. Seijuro gloated that if he was killed then he would be martyred as the greatest warrior that ever lived. It was only then he recognized The Orochi, The Emperor's Champion and a hero of legend that could kill him without martyring him. They fight in a duel and The Orochi defeats him. The Orochi asks Seijuro to command their armies, but he is offended at the dishonor of being demoted beneath The Orochi and would rather die. The assassin then presents his katana and offers Seijuro the chance to kill him if it meant recruiting him to lead their armies. Moved by The Orochi's courage and dedication to the Empire, Seijuro relents and agrees to help lead their armies.
While not seen, it is likely he helped lead the armies against the Blackstone Legion fortress.
A serious man who was proud of his skill and martial prowess and with good reason, Seijuro was ambitious but valued honor above all else. Not only an orochi skilled at one on one combat, Seijuro was an excellent battlefield commander, one that Ayu and The Orochi would rather recruit than slay.