The US specifically wanted to avoid the Soviets from entering the Pacific Front because they didn't want them having any possible claims to Japan and potentially having to split the land akin to Europe. Pretty quickly after the US occupation there was a sizable communist movement seeking to gain power through election where they expected the US to hold up their public statements of freedom and democracy. In the end though the US cracked down on the leadership and essentially destroyed the movement. Though pretty pathetic now, the Japanese communist party still receives a decent chunk of the vote, though obviously nothing to actually disrupt the neoliberal hell.