Usada, or Rabi~en~Rose, is revealed to the viewer to be Dejiko's rival. Her nickname may be a play on a number of things. "Rabi~en~Rose" may be a play on the common French saying "La Vie en Rose" which means "life in rose-pink". The Japanese expression "spend a life in rose-pink" means to spend a life without any worries. "Rabi" which resembles the English word "rabbit." replaced "La vie" to form a pun to mean "Rabbit in life without worries," which suggests her personality. Her original name is Hikaru Usada, which resembles Hikaru Utada (best known in the West for her theme songs for the Kingdom Hearts series) but that was officially commented as a mere coincidence since the story and names were decided before Hikaru Utada's debut in Japan. Her "Usada" surname also is a pun, as the "Usa" part is a shortening of the word "usagi", which means "rabbit" in Japanese.

In the original anime, she is seen as a normal girl who uses dice to transform into her bunnygirl outfit: a pink, white and red dress with large white rabbit ears and a large round cotton tail. Her parents left her to live on her own in an attempt to help her become an idol. Rabi~en~Rose does not end her sentences with a rabbit sound (typically pyo in anime) and is the only character with kemonomimi animal traits in the Di Gi Charat franchise not to do so.
(source: wikipedia)

She is very competitive and always is trying to start something with Dejiko. In some of the manga stories, however, it is shown tthat she really just wants to be her friend, and this is hinted at in various ways, often ending in a comedic gesture.