Sasaki Sukesaburō serves as a samurai retainer to Tokugawa Mitsukuni, the retired second daimyō of Mito Domain, traveling incognito across Japan. As one of Mitsukuni's two primary bodyguards, Sukesaburō exudes a fun-loving and energetic personality, contrasting with his more studious counterpart, Atsumi Kakunoshin. He accompanies Mitsukuni (disguised as a retired crepe merchant) on journeys to investigate injustices committed by corrupt officials, merchants, or gangsters.

Sukesaburō's duties encompass both investigation and combat. During confrontations, he typically leaps into brawls unarmed or in disguise alongside Mitsukuni and Kakunoshin against adversaries. These clashes culminate when Mitsukuni reveals his identity via an inrō case, leading to judgment on the antagonists. Sukesaburō's combat style relies on physical prowess, ensuring reliable protection for his lord.

In the animated adaptation *Manga Mito Kōmon*, the character is renamed **Kaiko**, maintaining his core bodyguard function. Kaiko is explicitly noted for extraordinary physical strength, while his partner **Tsuke** (representing Kakunoshin) excels in swordsmanship. Together, they protect Mitsukuni (Mitokomon) during travels to observe provincial governance, combat corruption, and deliver justice to citizens. Kaiko's strength frequently proves instrumental in overcoming adversaries and resolving mission conflicts.