Ichimatsu Matsuno holds the position of the fourth-born among the Matsuno sextuplets. His name originates from "市松" (ichimatsu), signifying "checkered," yet utilizes the kanji for "one" (一) following common male naming traditions. He resents misspellings of his name with the checkered pattern characters. During childhood, he exhibited a more serious, practical, and strong-willed disposition than his brothers. Marginally smarter and thriftier, he remained academically weak like his siblings. His behavior toward younger children fluctuated between sporadic kindness and equal violence or mischief. He frequently allied with Jyushimatsu in escapades, cementing an early bond. Group divisions consistently paired him with Jyushimatsu across manga and anime narratives. His endurance occasionally exceeded his brothers', notably when he nearly summited a building during a pursuit. As a teenager, he crafted a popular, extroverted identity called "Ichi." Insecurity undermined this facade, and his drive to distinguish himself from his siblings caused social burnout, shaping his adult persona. A defining moment unfolded when his future self counseled his teenage self to "be himself," solidifying his retreat into isolation. Adulthood cast him as the family's "lone wolf," marked by antisocial tendencies, half-lowered eyelids, untidy hair, and a slouched stance. He habitually wears purple hoodies and sweatpants. His pronounced fondness for cats eclipses his interest in people. Though his brothers deem him incapable of friendship, his seclusion arises from crippling self-doubt and emotional inexpressiveness. Symbolically, his heart manifests as a delicate glass object labeled "fragile," revealing profound vulnerability beneath his detachment. Confronting his teenage self unleashed violent self-loathing, prompting a suicide attempt and a subsequent effort to kill his younger self before intervention. Social struggles endure, evidenced when mimicking his past "Ichi" persona triggers physical and emotional collapse. His strongest bond persists with Jyushimatsu; he maintains constant proximity and reluctantly joins activities like serving as counterweight for a baseball bat. Choromatsu's quest for "normalcy" intimidates him, and despite both being middle sons, they share no mutual interests. He nurses unspoken animosity toward Karamatsu, potentially fueled by envy of Karamatsu's self-assurance, delighting in Karamatsu's misfortunes. His psyche materializes as a subterranean, cat-shaped furry mass symbolizing concealed self-consciousness. His animal motif remains the cat. In an alternate timeline, he alone avoided his brothers' weight gain. A gag in "Let's Get a Job" nods to a childhood manga where he became a company president by casting him as a factory overseer. When queried about deserted-island essentials or personal fetishes, he specified "a cat" and "cat paws."