I have to say the light novel is so much fun to read... :P liked the first chapter a lot; liked the second one, too.
out of the three (?) characters so far presented, I think I've started to like childhood friend a lot more than the others. yeah, she is described as plain (even with her character design), but there's something about her, I don't know. maybe it's the way she talks, the way her conversations with the main character seem so entertaining and fun to read (like being called a granny). reminded me a bit of Aoba Tsugumi, :P
on the other hand, the two siblings are an interesting pair, I guess. one is clueless about her situation and the kind of games she plays; the other one is too aware of her sister, so to speak. it makes for some interesting conflict, I would say; but I'm having a bit of trouble to find anything to like about them.
@Bonta Kun
I wouldn't want Rie doing yet another tsundere kind of role. haven't we got enough of those?
on the other hand, Haruka Tomatsu would be the perfect choice for imouto. :P