February 11th is celebrated as Natinal Foundation Day. According to Japanese mythology, Emperor Jimmu, the first emperor of Japan, ascended to teh throne and founded the imperial line on this day. His reign is said to have started in 660 B.C. It was celebrated as kigensetsu, the day of origin, only until the end of the Second World War, and was discontinued after the war because there’s no real historical basis for it. But it was designated a national holiday in 1967.