There's not a lot you can say about Kira without spoiling a good deal of the story. ^^; Basically, he's Setsuna's only true friend (besides Sara), and he's always protecting and watching over Set-chan.  He's also most always seen holding a book, which I think is cute. ^^;   Kira's not  my favorite character, but he's probably one of the most complex of the bunch.  I could write scores about him, but like I said, that'd be a huge spoiler, so that's all I'm going to write. ^^;