Osomatsu Matsuno, eldest of six identical brothers, asserts a self-designated leadership role marked by mischievous impulsivity and sporadic displays of concealed fragility. Childhood portrayals in *Osomatsu-kun* depict him orchestrating pranks that blurred camaraderie and cruelty—stranding Choromatsu on a train, trapping Ichimatsu in a closet—yet his fleeting remorse surfaced through acts like shaving his head following family distress or revealing loneliness during a temporary adoption. As an adult NEET in *Osomatsu-san*, his gambling obsessions and evasion of responsibility mask insecurities symbolized by a grimy red ball representing suppressed self-awareness. Though he jokes about desiring solitary freedom, storylines like "The Melancholy of Osomatsu" expose his dread of abandonment when siblings contemplate independence, contrasting his carefree facade. Sibling dynamics shift across eras: childhood dominance over Choromatsu evolves into rivalry with the adult brother’s growing pragmatism. He fuels chaos with Jyushimatsu, engages in psychological sparring with Todomatsu, and needles Ichimatsu’s sardonic outlook. Despite proclaiming authority, his unreliability emerges when prioritizing self-interest—betraying brothers for petty gains or neglecting to shield them from fallout. The 2019 film *Mr. Osomatsu: The Movie* forces him to confront stagnation during a high school reunion, exacerbating existential dread as peers outpace his aimless adulthood. Season 3’s "The Way Home" amplifies collective anxieties about maturity, as post-wedding discussions underscore his discomfort with societal milestones like parenthood. Visually, his design anchors the siblings’ color-coded identities: childhood dental flaws and a bowl-cut mature into adult features distinguished by a toothy grin, upturned nose, and red-accented hair. His red attire reinforces his role as the baseline from which other brothers’ variations derive. Labeled a "Miraculous Idiot" for persistent immaturity, rare introspective flashes—guilt over past harms, half-hearted attempts at sibling support—hint at buried empathy, though these gestures often dissolve into comedic reversals. His oscillation between bravado and covert dependency underscores narratives of stunted growth and the fraught endurance of fraternal ties.