Naomasa is a tall man with short, black hair and somewhat rectangular black eyes.
As a member of the police force, he is normally seen in his uniform, which consists of his signature tan overcoat and matching hat, underneath which he wears a black suit, a green tie at his neck with matching slacks, and dress shoes.
Following the Paranormal Liberation War, Naomasa has grown out a light goatee and he has developed eye bags, likely from a lack of sleep and rest. He has also been shown wearing armoured police gear.
Gallery
Detective Uniform
Personality
Detective Tsukauchi is an earnest, hardworking individual who has earned the right to be a close friend of All Might, enough so, that he was even entrusted with the truth about One For All and the former's true form.
As a detective working with the law, Naomasa is strict and does not approve of vigilantism, which, despite having heroic intentions, is still illegal and therefore makes them Villains. However, despite vigilantism being illegal, he is shown to be grateful for The Crawler helping to protect the Tokyo Sky Egg from Bomber villains.
He appears to have a close relationship with All Might, as he even leaked sensitive information to the hero just because he felt it was the right thing to do. He is shown to be hesitant with requesting All Might for help, even when there are thousands of lives at stake, although he decides to go against police procedure to let All Might rescue the Tokyo Sky Egg.
Naomasa also cares a lot for his sister, Makoto, as shown when he desperately cried for help to All Might to rescue his sister. Makoto would often tease her brother and challenges authority (although not to the point of committing anything illegal), which would annoy Naomasa quite a bit. However, the two can get to the point of argument, such as when Makoto argued that Pop☆Step shouldn't be treated as a villain after several bombings, while Naomasa tells her to quit arguing for the sake of it.
Abilities
Deductive Intellect: As a police detective, Naomasa likely possesses above-average powers of deduction.
The kanji in Naomasa Tsukauchi, Nao "直"(lit. straight), and masa "正" (lit. correct, justice, righteous). Tsuka "塚" (lit. mound) and uchi "内" (lit. inside, within).