Sakamoto, a black cat, lives with Nano Shinonome and her creator, the Professor. Originally named Taisho, he belonged to Nakamura-sensei before moving to the Shinonome home. This shift followed his tumble from Nakamura-sensei's window and subsequent discovery by the Professor. He received his current name when the Professor found him inside a box labeled "Sakamoto."

A red scarf made by the Professor grants Sakamoto the ability to speak human language. He is roughly 20 years old in cat years, placing him older than both Nano and the Professor. Sakamoto frequently stresses this age gap and demands respect, though his housemates often disregard this. He adopts a condescending, middle-aged tone in his speech and dealings, especially directed at Nano and the Professor. Despite this demeanor, he exhibits typical feline instincts like chasing small animals or playing with toys. Sakamoto tries to hide these actions to maintain his mature image, but sometimes succumbs to them involuntarily.

He endures the Professor's constant pranks and physical antics, including booby traps and makeshift contraptions. These experiences showcase his patience and his role as a reluctant caretaker within the household. While maintaining a facade of aloofness, he slowly forms connections beyond the lab, such as tolerating Yukko Aioi's enthusiastic reactions to his abilities. His relationship with Nakamura-sensei remains defined solely by his origin.

Sakamoto's role remains consistent as a dry-witted observer whose attempts at dignity contrast sharply with the absurdity surrounding him.