This is a disingenuous strawman. "Japan First" doesn't have to mean your naïve interpretation of some maximally xenophobic isolationism. If the US bases are good for Japan, then it's perfectly "Japan First".

Some people might disagree—certainly plenty of right-wing Japanese do disagree—but many also believe that the US alliance and the bases are critical to Japan's greater sovereignty and prosperity. Without the security treaty and cooperation, Japan would on their own against China, diverting far more funds to defense and accepting much higher security risk.