Usa-chan (aka Ousi-chan or Bun-Bun) is a pink plush rabbit and one of Mitsukuni "Honey" Haninozuka's possessions. It was hand-made by Honey's deceased grandmother, and although it's just a toy, Honey cares for it as if it is alive, talking to it and having it join him for his regular cake indulgences. At times, the expression on its face changes to show emotion.
Story
While Usa-chan never speaks, it does play an important role in several anime episodes. The first occurrence is in the episode Ep 13 - Haruhi in Wonderland! where Usa-chan portrays the character of the White Rabbit from the classic children's book, Alice in Wonderland]. It is Usa-chan who tempts Haruhi Fujioka "down the rabbit hole" that appears in the floor of Music Room 3 and brings her into an Ouran Academy that resembles the Wonderland story in several ways, including characters and some of the plot. In Ep 12 - Honey's Three Bitter Days!, the toy rabbit is accidentally stained with tea, causing Tamaki, Hikaru and Kaoru to panic, though this is primarily due to Tamaki's tall tales about the loli-boy's reaction to being awakened early and never to Usa-chan directly. After Honey graduates high school, Takashi "Mori" Morinozuka only allows him to carry Usa-chan every three days.