To get a 1 year Z visa you need to first have a valid work permit. Once you get your work permit (1 year), and renew next year, you wont have to do anything special or go anywhere particular – and the paperwork is far far easier to renew than to get the initial work permit. The reason they give you a 1 month initial visa would likely be they want to give you a limit to get your residential registration and work permit authorization complete within a reasonable time, rather than let it slide since you’ve already got your visa – in this way they guarantee you’re going through a legitimate workplace where they’ll have to end up paying social benefits/tax/etc to the government. Maybe there used to be some “scam” companies that would set people up with a visa but not actually employ them, charging them for the service, and this relatively new process helps kill that loophole.