The US forced the Japanese to rewrite their constitution with input from the US, the Japanese government and from non governmental groups. US demands were mostly to make it harder for militarists to seize power. Probably the biggest changes was press freedom and the legal rights of women.

My impression of the place is you have a modern industrial society replacing large parts of the preexisting feudal culture. Important, Japanese feudal culture is not the same as western Europe feudal culture. More face culture, less shame culture. And Japanese aren't as much prudish, as conservative and obsessed with decorum.

Still can't find the source of it, but I remembered more details behind the "culture rewrite" hypothesis I read the other day. That source argued that US didn't just defeat Japan, but it thoroughly broke the cult of emperor that existed there until end of WWII, and thus (implied) from the POV of the whole society, the west slew their god, and became a new role model.

The Japanese culture is still very different from the Western one. It's more similar to South Korea probably, perhaps even China in some ways.