Kazuma Sakamoto, Isami Hanaoka's maternal uncle and younger brother of Reiko Hanaoka, works as an Oedo police detective. His cases routinely overlap with Isami and her friends' activities, prompting frequent visits to the Hanaoka residence for investigations that conveniently align with mealtimes.

Initially single and romantically clumsy, Kazuma displays persistent yet awkward courtship efforts. He nurses a visible attraction toward Ruriko Serizawa, evolving into a mutual relationship as the series advances, forming a recurring thread in his personal journey.

Professionally, he tracks incidents tied to the Black Tengu Organization, positioning his police work within the central conflict. Kazuma also shares ties with Silver Tengu, a high-ranking antagonist whose actions occasionally reveal ambiguity.

His name echoes the historical samurai Sakamoto Ryōma, famed for Bakumatsu-era reforms, though Kazuma's modern detective role lacks direct parallels to this legacy.