Naruzou Machio serves as a bodybuilder and personal trainer at Silverman Gym, regularly coaching students from Koyo Girl's Academy. He presents a deceptively average or slender frame when clothed in his blue and white tracksuit. However, flexing instantly transforms him, revealing an incredibly muscular, bulky, and defined physique that violently tears through his clothing, leaving only his Speedos intact. This explosive transformation starkly contrasts his fair skin, short messy black hair, blue eyes, and handsome face. He possesses precise muscular control, allowing him to selectively bulge specific body parts through his garments.

Machio exhibits a kind, helpful, and dedicated personality, consistently offering encouragement over mockery to those demonstrating genuine effort. He maintains a charming demeanor and deep knowledge of bodybuilding and exercise. A recurring comedic trait involves him flexing and bursting out of his clothes at the slightest muscle-related trigger, seemingly unaware of how his resulting near-nakedness unsettles others. He demonstrates no shame about public near-nudity, even contemplating boarding planes in just Speedos if allowed.

His background includes exceptional muscular development starting in high school where he played American football. Post-graduation, he studied sports theory at a U.S. university and discovered bodybuilding, leading him to train under the renowned bodybuilder Harnnold Dogegenchonegger. They lost contact after separate incidents destroyed their phones but plan to compete someday. Machio's story begins when he meets Hibiki Sakura during her first visit to Silverman Gym; his appearance convinces her to join despite her reservations about "macho men." He guides Hibiki, Akemi Soryuin, and others through foundational exercises like bench presses, frequently showcasing his physique during sessions.

Machio's physical abilities far surpass normal human limits. He effortlessly crushes specialized hand grips only 100 people worldwide can close single-handedly. Early in training, he benched 100kg and curled 50kg dumbbells. Beyond raw strength, he achieves "divine muscle mastery," emitting overwhelming machismo capable of dominating bodybuilding competitions like the Harnnold Classic with a single pose. He also serves as a qualified kannushi (Shinto priest) and head priest of Masura Shrine. His pectoral muscles twitch during spiritual disturbances, enabling him to perform "exercisms" to purify spirits, as demonstrated when he subdued and purified the ghost Toyoda Tadakatsu.

His relationships include Hibiki Sakura and Satomi Tachibana, who both develop crushes on him, though he remains oblivious to their affections. He shows particular interest in Hibiki's natural strength. He collaborates with Akemi Soryuin on explaining workouts and diets. He maintains friendships with childhood friend Nana Uehara and high school friend Sakura Ibuki. He shares mutual respect with mentor Harnnold Dogegenchonegger and colleague Koharu Utsunomiya. The purified ghost Toyoda Tadakatsu joins Silverman Gym adoringly without Machio realizing his non-corporeal nature.

Notable trivia includes charging $50 hourly for personal training, appearing in Silverman Gym commercials with Julius Reinhold, and developing a cosplay hobby after summer Comiket. His full name is a pun on the phrase "let's get macho" (マチョなるぞ), with "Machio" combining terms for "city/street" and "hero/manly," and "Naruzo" meaning "ringing" and "create/structure." As Masura Shrine's head priest, he is revered as "The Great Muscle God" (マッスル大明神) in religious circles.