The uchide no kozuchi, literally “small hammer for beating,” is an item with many positive associations in Japan. It is variously translated as “magic mallet,” “miracle mallet,” or “lucky hammer.” When it is wielded by Daikokuten, one of the shichifukujin seven lucky gods, it has the ability to grant wishes. When it was waved at folk legend of Issunboshi, the One Inch Boy of a Japanese folk legend, it made him grow into a normal sized human being.
Magic mallets have a long history in Japan; the eighth century Nihongi history tells how mallets made from camellia wood were used to battle savages. They were also used to dispel evil spirits during New Year ceremonies during the Heian (754-1185) period(1).
Given that uchide no kozuchi can fulfill wishes, battle bad guys and drive away evil spirits — not to mention make short people grow — it’s hardly surprising that they’re a popular decorative motif on kimono and other textiles, greeting cards, porcelain wares, and yes, hashioki.
Please refer to my post on Issunboshi from March 2016, and look for a future post on Shichifukujin.
(1) Baird, Merrily. Symbols of Japan: Thematic Motifs in Art and Design. New York: Rizzoli International, 2001, pp. 261-262.