ALICE 19TH (Arisu Naintinsu), by Yuu Watase. First published in 2001, and first published in North America in 2003.
PLOT:
Alice Seno is a quiet, pleasant girl, the sort of person who wants to please others at the expense of her own happiness. She's nothing like her older sister Mayura, who is beautiful, lively, and the darling of both her parents and classmates. Alice has a crush on one of her sister's classmates, Kyo Wakamiya, and is crushed when her sister starts dating him.
At the same time, Alice encounters a strange bunny, who turns into an equally strange little girl who tells her she is a Lotis Master. Alice doesn't quite understand what this means until some hasty, heated words from her cause her older sister to disappear and the boundaries between this world and another begin to break down.
