This does sound like a perfect use case for "AI" tools however. It's literally style transfer.

Edit: though maybe grounds for a "rounded corners" style lawsuit, given the business style of the folk we are dealing with here.

Maybe not for the full japanese characters set, but for an existing game, they could do it for the subset of characters they are using.

I don't think that's practical, because the subset would still be quite large. I did a quick analysis of the Factorio localiization files and found more than 1200 unique characters