I find it incredibly funny how he has his mind full with that Kei girl and having a girlfriend in general. Let's just forget the fact that he's basically in a live-or-die situation where he battles freaking aliens in some sort of Battle Royale cage setting.
Hopefully that Kei girl either goes to the background or simply dies, because all she does is cause sexual frustration among the main cast. She's not really being all that subtle herself, jabbering about Masaru non-stop even though she knows that Kei has the hots for her.