So we need Spain, with a population between 5 and 8 million people during the 16th century, to completely subyugate Japan (at least in a cultural manner), with a population around 12 million in the same century, without "guns" (the Japanese were very apt and quick to adapt the European technology, as they had been only slightly behind) nor "germs". I am not even sure we could have outproduced Japan, unless we used the resources of the whole American empire for the task, so the "steel" is dubious.
I really don't see it.
I'd like to note that during the Spanish domination of America, Spanish was not the majority language. Each one of the viceroyalties had a normativized version of one of the native languages as coofficial. While there had been a growing adoption of Spanish by the natives, this process had been slow, and not enforced. This changed mostly with the independencies, where the creole minorities who had seized the power began to enforce the linguistic hispanization of the population.
Why is this relevant? Because even on the event of a Spanish conquest of Japan, Spaniards would not be set as daimyo lords nor as imperial bureucracy, due to the Japan and Spain being on very similar level of social/technological development. Not unless the native Japanese bureaucracy and nobility was exterminated, which was not the modus operandi of Spanish conquest, nor it would even be remotely feasible. And without a sizeable social group of Spaniards atop the government in Japan, there is not going to be a linguistic substitution, as there was in America.