The Second Monday of January is a national holiday where 20 year old men and women celebrate coming of age (adulthood). The age of 20 is also when people are legally allowed to vote, drink, and smoke.
Women celebrate the day by wearing furisode kimono and men generally wear suits though occasionally tey will wear dark colored kimino's.
A furisode (Japanese: 振袖, furisode) is the most formal style of kimono worn by unmarried women in Japan. They are made of brightly colored silk and have long sleeves generally between 39-42 inches in length. By wearing a furisode, a young woman signifies that she is both single and a legal adult, and thus available for marriage. Furisode are generally very expensive (around $10,000) so most women rent them rather than buy them. The average girl generally doesn't even know how to properly put one on and go to kimono kitsuke to have them put on.