How do I resign before my full-time start date when my employer already filed my visa change?

Hi everyone. I'm writing here because I’m in a bit of a complicated situation and would really appreciate some advice. (And before you target this as AI slop, I did use for clarity as English is not my mother tongue. The issue is real and I need to get it sorted out soon).

I have already been working for this company part-time, and recently they hired me for a new full-time position and started the visa / change of status application process for that role.

However, my situation has changed and I now need to withdraw before the official start date of the new full-time position.

So to clarify: I am not resigning from a position I already started, but rather withdrawing from the new employment arrangement that was supposed to begin soon, while the company is already handling the immigration process.

I’m mainly trying to understand:

– whether this is considered a resignation or simply withdrawal of the new contract

– how to properly give my resignation / communicate this to the company

Has anyone experienced something similar in Japan?

What is the safest way to handle this with HR?

Thank you so much for any advice.