Ichikawa Sukefusa serves as an antagonist in the series, acting as the assistant to the Shugo, or governor, of Shinano Province. His character is defined by a calm, serious, and often unsociable demeanor, yet he demonstrates a consistent and deep-seated loyalty to his lord, Sadamune Ogasawara, providing assistance whenever needed. Rather than a simple master-servant dynamic, their relationship functions more as a partnership, where Sukefusa trusts and supports Sadamune but is not afraid to speak plainly or act on his own judgment if he believes his lord's approach is flawed.

Role in the story is primarily as a strategic adversary to the protagonists. Following the downfall of the Hojo clan, Sukefusa aids Sadamune in efforts to eliminate the clan's survivors. His intelligence and tactical mind allow him to anticipate and predict enemy strategies. A notable confrontation occurs when he discovers Tokiyuki Hojo and Kazama Genba during a robbery attempt. Using his unique sensory abilities, he traps them, leading to a battle that ultimately ends with the pair escaping, though not without consequence for Sadamune. Later, he is appointed as a guard to the kokushi, a position where he continues to protect his charge and gather intelligence on Tokiyuki for Sadamune. As the conflict drags on, frustration leads Sukefusa and an ally to break their ties with Sadamune and oppose him directly. Sukefusa also voices his displeasure with the heavy taxes imposed by the official Shinano no Kami Kiyohara, going so far as to deliver a complaint on Sadamune's behalf.

The character's most notable ability is an enhanced sense of hearing, which he uses both offensively and for information gathering. His hearing is sharp enough to detect footsteps, voices, whispers, and faint noises, and he can even listen to heartbeats to determine if someone is lying. In darkness, he can use his hearing like sonar to perceive his surroundings. This skill extends to using the earth as a conductor; by placing an ear to the ground, he can discern the number, ages, and actions of people nearby based on vibrations. In combat, Sukefusa is an expert swordsman who relies on his hearing to track an opponent's movements and land his attacks. His appearance is distinctive, characterized by long, narrow eyes, large ears that allude to his heightened sense, and a unique hairstyle that gives the impression of a second pair of ears on his head.