Shinba over here feeling that oh-so fun complex emotion. His sister has grown and improved, but in exchange the sister he was so used to isn't there anymore. On the one hand that's a good thing, on the other it's a change you almost don't want. It might also be aggravating his own frustrations with his much slower attempts to change and improve himself, given she managed to get like this after only a month.
As for Hizumi, given that sad look... I almost feel like she wants to be able to help him, but is maybe afraid of "ruining" him somehow. Just the impression I'm getting.