Converting from dependent visa to work visa after reaching Japan. Who applies typically? Me or the employer?

Planning to reach Japan in a few weeks on a dependent visa.

I have an offer from a Japanese company which will be used in the application for the gijinkoku work visa. Before I ask the HR what they expect, I just want to know what is the typical way to get apply for this visa?

Does the company apply or do I apply (on my own) or do I apply via an agent? If the company asks me to apply then I will do it, but should I apply on my own or via an agent?

So far, based on the communication with HR a few weeks ago, they have told that they will provide me the documents once I reach Japan. I haven't discussed further with them yet.