In this case I take a completely opposite view to Srin Tuar. Yuuji is lucky Kazuki has anything to do with him at all. He has been stupid, ugly, selfish and rude for ten episodes. (I dislike both his character design and his voice acting, which doesn't help.)
Kazuki and the gun-toting sister are what make this show, for me. Contrary to the case of Yuuji, I love Kazuki's character design and the way Kanda Akemi (Meme in Kamisama, Asuna in Negima, Rihoko in Witchblade) is doing her voice.