Since the early 1990s, Steven Reed and Gary Cox have changed our understanding of Japan's multimember SNTV electoral system by high-lighting its institutional effects similar to what is known as Duverger's law in the Anglo-American context. Both Reed and Cox presented evidence to show that Japan's M-member districts tended to produce competition among M+1 candidates, thus claiming that a generalization of Duverger's law, called “M+1 rule” exists and applies to the Japanese case. This paper reevaluates Reed's and Cox's claims. We offer some additional evidence to demonstrate that the findings of these two studies are reconcilable, both pointing to the basic pattern of Japanese voters' strategic behavior under the above electoral system. We, however, also address an issue left unexplored in these previous studies, namely the role of political parties. Under Japan's multiparty system, party labels matter in elections: while Japanese voters are generally willing to abandon the candidates without affiliation with the established parties, the partisan effects produce constraints for voters' strategic coordination for both informational and ideological reasons.