I was unaware of migrant labor in Japan. I would *guess* it's more for elder support than factory work.
Japan's managed to relocate their factories to places close to where those goods are consumed. I remember it being a bit of a battle to get them to put car and tire factories in the US, but IMO it's been a successful strategy for a country where both the consuming age group and the factory labor age group are aging out. Kind of a pity that China didn't take the same approach as they'd be less dependent of blue water shipping (and the US's growing disinterest in protecting that). I've had that conversation with a couple of Chinese friends (why China didn't do like Japan) and one of them told me "China didn't get rich fast enough." which I think might be spot on. Without getting into internal Chinese power dynamics which I don't really have a grasp on anyway.