Karamatsu Matsuno, the second-eldest of the Matsuno sextuplets, remains unexplored in *Osomatsu-kun: Iyami wa Hitori Kaze no Naka*, though other media expand his narrative. His childhood blends carefree energy with impulsive antics, marked by a crybaby reputation. Bravado masks vulnerability, often plunging him into comedic misfortunes or injuries. He devours meals ravenously, occasionally to the point of discomfort, yet displays unexpected tidiness, such as nursing overheating gadgets. Mocked for perceived emptiness via "karappo" puns, he counters with artistic talents in painting and sewing.

Adolescence introduces chronic acne and a quiet struggle for individuality amid shifting sibling dynamics. His timid attempts to mediate family tensions rarely succeed. Adulthood reshapes him into a leather-clad, sunglasses-wearing figure radiating misplaced confidence. Dramatic speeches and cringeworthy charm earn him the derisive nickname "Kusomatsu" from brothers, though fleeting vulnerability surfaces, like frustration over their mockery.

His bond with Todomatsu fuels childhood escapades often ending in mutual blame or failure. While primarily a source of humor, later stories delve into his resilience and introspective moments. The larch tree ("karamatsu") inspires his name, tying to emptiness-themed jokes. Trivial notes include a preference for spicy flavors and a fictional future marriage depicted in a one-shot tale.