TV-Series
Description
Choromatsu Matsuno is one of six identical sextuplet brothers. His name derives from the Edo-era term "chorochoro," denoting fast-running, foolish children, merged with "choroi" (simple/easy).

In childhood, he displays cleverness yet profound selfishness, acting impulsively and fleeing situations. He judges others quickly, boasts about his capabilities, and possesses a short temper. His agility makes him excel in sports, but he shows minimal concern for his brothers' well-being, prioritizing results over their feelings.

He forms a close partnership with Osomatsu, frequently collaborating on mischief. This relationship involves power struggles—Osomatsu sabotages others while Choromatsu seeks dominance. When Osomatsu is temporarily adopted by a wealthy family, Choromatsu assumes leadership and becomes tyrannical, whipping his brothers and father until Osomatsu returns and restores order.

A defining childhood incident occurs in the "40 Years" story. After Choromatsu alters a map to retaliate against Osomatsu’s attempt to abandon the brothers, Osomatsu becomes trapped in a cave. During Osomatsu’s 40-year absence, Choromatsu develops severe guilt, resulting in stunted physical growth and mental regression to a childlike state. He repeats phrases like "Anonee, I'm Choromatsu" and recites the alphabet.

As a teenager, he wears thick glasses to project a studious image but remains academically poor, hiding erotic magazines inside textbooks. His posture stiffens, and he becomes a clumsy teacher's pet, behaving obnoxiously toward adults.

In adulthood, he presents himself as the most logical and responsible brother, often acting as the straight man. He expresses concern over their collective unemployment and NEET status, suggesting he should replace Osomatsu as the eldest. This demeanor masks insecurity and bluffing; his "responsible" persona is not his authentic self, and he consistently reverts to complacency. He overthinks situations, struggles to conceal emotions, and harbors an obsession with idols like Nyaa and Totoko, admitting his interest lies solely in fantasizing about the girls rather than their music. He retains his teenage interest in sexual content.

In the alternate future ("Osomatsu-kun Grows Up"), he becomes a police officer, contrasting his NEET adulthood in other continuities.

Key relationships include his rivalry-driven partnership with Osomatsu, his role as an instigator among the brothers, and his fixation on female idols. He also experiences alienation scenarios, such as being abducted by aliens alongside Osomatsu.

Physically indistinguishable from his brothers as a child, adult Choromatsu adopts green-themed clothing, a downward-turned triangular mouth, smaller pupils, and lacks cowlicks in his hair.