Japanese. Usagi (兎) = Rabbit. The character comes from a pictograph of a rabbit. Often written in katakana or in hiragana instead.

Kotowaza (Japanese expressions) related to usagi:

Kotowaza: Usagi shi sureba kitsune kore wo kanashimu.
Literal translation: If a rabbit dies, a fox mourns this.
What it means: When a group member dies, those within the group (friends and relatives) mourn.

Kotowaza: Usagi no nobori-zaka.
Literal translation: Rabbit's uphill.
What it means: When events happen at a fast and steady pace.

Kotowaza: Usagi no fun. / Usagi no kuso.
Literal translation: Rabbit's dung.
What it means: An analogy for when events happen intermittently and progress is slow. The kotowaza comes from the fact that rabbit dungs are small round dots.

Usagi is also an animal in the Chinese Zodiac, which was introduced to Japan by Buddhists.

Also the rabbit on the moon is supposed to be making an immortality medicine using a hammer according to Japanese culture. Recently some have been calling it a mochi instead of a medicine.

Once upon a time, a group of Japanese Zen Buddhist monks really liked to eat rabbits but were in a moral dilemma because it is was against their religion to eat land animals. To circumvent this problem, rabbits became classified as birds, considering the fact that rabbits have long ears. With this classification, the monks were Ok for a rabbit meal. This stuck with Japanese culture, and to this day, rabbits are still counted as 1wa, 2wa, 3wa... as if they are birds, as opposed to the usual counting standard of non-bird small animals, which is 1piki, 2hiki, 3piki...