Kensei is a tall, muscular man with sharp features, short light-gray/silver hair and brown eyes. He has a tattoo of the number "69" on his chest; the "6" represents his last name, "Muguruma," which uses the kanji for "6" in it, while the "9" represents the 9th Division, which he currently leads. He wears a dark purple A-shirt with a white trim, in addition to green cargo pants, black combat boots, and a pair of orange fingerless gloves. He also has a series of piercings, with one on his left eyebrow and three on his left ear.
During his initial time as a captain, Kensei had longer front bangs, which hung over his face. He wore a sleeveless shihakushō that was open on the front, exposing his chest and tattoo, and tied it with a rope belt. He also wore a sleeveless haori and a pair of fingerless black gloves that covered most of his forearms. Seventeen months after Aizen's defeat, he returns to wearing this look, albeit with a less open shihakushō, a new metallic belt and mussed up hair.
Kensei is a serious and decisive individual, though he is easily annoyed and is rather temperamental, often to a fault. He is greatly annoyed by immaturity, evident when Orihime infiltrates the Visored's hideout and jokingly asks where the bathroom is; Kensei is noticeably annoyed, only calming down when Lisa Yadōmaru and Love Aikawa remind him that it was only a joke. He is most frequently irritated by Mashiro's childish behavior, once noting that she has the uncanny ability to aggravate him even when she is asleep. His aggressive behavior is particularly noticeable in combat. At one point, he confesses that he is not mature enough to hold back, even against a child. Despite this, Kensei is at times a caring individual, though his attempts at being kind are often offset by his aggression. This is displayed when he tries to cheer up a young, tearful Hisagi, albeit in a manner reminiscent of a military drill sergeant.