The Yomiuri features a seat-by-seat rundown on the Upper House election (it's not available on its web site; let's what the Asahi does when it comes out with its own survey, as it must). Its conclusion is that the "ruling parties [are] likely to lose [its] seat majority" and (in the Japanese-language version) "the possibility is high that the number of seats that the LDP retain in the district and proportional representation elections may wind up in the lower half of the 40s unless it can turn back the winds that are blowing against it." This does not make my off-the-cuff over-under 45 call any less valid; elections tend to tighten up as the voting day draws near. I asked a veteran of many an election campaign about this phenomenon, and he came up with this analogy:
Let's say you're going to have dinner one month from now, and you're given a menu and asked what you want. There's steak, but there's all this other stuff, and you're not sure, you think you might have something else this time. Now, a month later, you actually walk into that restaurant, and they give you the menu and you see the steak and you wind up saying, oh, I'll have steak. (he's an American) You go with what you know.
Of the all-important 29 single-seat elections, the Yomiuri survey shows the DPJ ahead in eight and the LDP in only two, and the two parties running neck-and-neck in the other 19. The silver lining for the LDP is that the proportion of undecided voters among its supporters are generally (though not uniformly) substantially higher than the same proportion for the DPJ and its supporters. The LDP has a greater upside here; thus the caveat in the tentative conclusion in the Yomiuri article. So how strongly will its supporters want to punish the LDP? This question seems to be just as important as the non-aligned turnout and how that in going to break.
A look at the details yields some clues about post-election LDP maneuvering, most likely necessary, for a working majority. The Yomiuri survey lists seven unaffiliated candidates in six electoral districts who have excellent to reasonable chances of winning. Of the seven, only one is supported by the LDP while one other is a conservative candidate who failed to gain LDP authorization but is running anyway. The others are supported by the DPJ (plus in many cases the People's New Party as well; more on that later). Moreover, the conservative candidate is running neck and neck with the LDP incumbent and a DPJ-supported unaffiliated candidate, so a win by this unaffiliated conservative will be a wash at best for the LDP. It looks like there won't be many unaffiliated newly-minted Upper House members waiting for the LDP to come calling with its basket of goodies.
The PNP seems to have cast their lot with the DPJ if campaign alignments are any indication. The PNP is supporting the DPJ candidate in most of the electoral districts where it is not fielding its own candidates. More important to PNP fortunes, in single-seat Shimane Prefecture, the DPJ has gone all in for PNP candidate Akiko Kamei, the daughter of Lower House member Hisaoki Kamei (the other, gentler PNP Kamei). Ms. Kamei is gaining on the LDP incumbent, and could give the PNP a real coup in the district seat elections. Yes, politicians will change their minds about anything to get elected (see: Rudy Giuliani and Mitt Romney), but it is going to be difficult to forsake your allies so soon after the war. Moreover, the PNP set the bar high when it demanded a revision of the Post Office privatization package as the condition for cooperation with the LDP.
So, barring unforeseen major events (like another political scandal erupting), I expect that the LDP will edge back up. But given the slim pickings among the unaffiliated candidates and the intransigence on the part of the NPP, the overall picture still looks like a decidedly uphill battle for a working majority in the Upper House.