Hyakusuke is the fiercely loyal close companion of Keiichiro Tokugawa, whom he considers his best friend and addresses as "boss." He readily offers assistance whenever Keiichiro or Otomi requires support.

Physically, he sports a top-knot hairstyle and gray eyes. His attire includes a purple scarf around his neck and a sleeveless yellow long kimono jacket featuring fur trim. Thin red arm bands adorn his upper biceps. A thick brown belt encircles his waist, connected to a chain extending toward his back, worn over brown baggy pants. He completes his outfit with arm guards, tabi socks, and sandals.

Intelligent yet lecherous, Hyakusuke channels his strong fascination with Western technology into inventions like a specialized telescope. He frequently uses this device with Keiichiro to observe women at the Cherry Blossom Baths, establishing his reputation for inappropriate behavior. This preoccupation recurs when he reluctantly agrees to watch Kiriko in exchange for a promised sexual favor from Chiharu.

Hyakusuke witnessed the Kuyama Alliance's surrender to Keiichiro Tokugawa. His relationships extend beyond Keiichiro: he harbors an unreciprocated romantic interest in Chiharu, the half-fox demon, openly admiring her despite repeated rejections. He holds deep respect for Iga, Keiichiro's retired ninja caretaker, consistently saluting her as a sign of deference, and shares a relationship of mutual respect with Asai.