Osomatsu Matsuno, eldest among six identical brothers, maintains a consistent core identity while adapting subtly across different portrayals. As a child, he asserts himself as the self-proclaimed leader of his siblings, combining bold confidence with a sharp taste for mischief. His schemes often target vulnerable figures like Chibita or Iyami, yet he reveals flickers of insecurity when confronted with repercussions or loneliness. Childhood designs alternate between lean and rounder body types in different versions, featuring a bowl-cut hairstyle with upturned strands and recurring dental flaws like cavities as visual trademarks. His personality weaves between teasing aggression and sporadic guilt—shaving his head to atone for family discord or regretting attempts to abandon his brothers for adoption.

Teenage iterations preserve his youthful appearance and troublemaking habits, including public teasing of girls, while emphasizing his persistent role as both instigator and de facto eldest sibling.

Adult depictions present a more relaxed attitude despite his continued claims of authority. Now a NEET沉迷 gambling, he chases quick thrills through horse races and pachinko, frequently pilfering siblings’ money to fund these habits. Though skilled at manipulating brothers for personal gain, he sporadically shoulders reluctant responsibility, acknowledging—yet often neglecting—his role as their caretaker. His adult design adds reddish hair highlights, a prominent toothy smile, and subtly reshaped facial features compared to younger versions.

Collaborative works like Japan Racing Association shorts integrate his gambling fixation into narratives exploring horse-racing culture, aligning with established traits. Throughout all portrayals, Osomatsu embodies a contradiction: self-centered impulsivity clashes with buried familial devotion, his brash persona deflecting deeper reflection while fueling comedic friction among siblings.