Oval, white with a blue caricature of a rabbit holding a fan (Chōjū-giga)

Chōjū-jinbutsu-giga (Chōjū-giga in short) is a famous set of picture scrolls that belong to the Kōzan-ji temple in Kyoto. The pictures depict funny scenes where animals (rabbits, monkeys and frogs) act like human beings. These anthropomorphic stories date back to the 12th and 13th century. The Chōjū-giga is often considered as the first Manga.

http://en.wikipedia.org/wiki/Ch%C5%8Dj%C5%AB-jinbutsu-giga

http://www.kokingumi.com/ChojuGiga/ChojuGigaScroll.html

Images of rabbits decorate many Japanese objects including a lot of hahsioki.

Rabbits are popular because in the Japanese folklore a rabbit pounding rice is said to live on the moon. He is making mochi (rice cake) for the festival of the moon in Automn (O-tsuki-mi). Some spots on the moon surface form indeed a shape that can be interpreted as the image of the moon rabbit working the rice.

The rabbit or hare is also one of the twelve Chinese zodiac signs which are also used in Japan. In the Chinese zodiac, it's the year of birth which determines the sign as follows :

http://en.wikipedia.org/wiki/Moon_rabbit

http://www.hashioki.com/