Regarding timing of Japanese residence

Hi, I'm a Japanese citizen that is moving back to Japan from the US.

Given that I'll be taxed on my global income as a Japanese citizen the moment I become a 居住者, I'm wondering exactly at what point in time that determination is made.

When I read articles such as the following, it seems that it is intentionally vague as it states it is based on my 「生活の本拠」, which is not simply about having an address, but encompasses multiple facets such as employment, location of assets, etc.

https://www.nta.go.jp/taxes/shiraberu/taxanswer/shotoku/2012.htm

Let me give a hypothetical situation that mirrors my own:

I tell my company that my move date to Japan is December 15th. It is a fully remote company that will take care of the paperwork and salary adjustments and deem me an employee residing in Japan starting December 15th.

Prior to this date, I take some time off and move to Japan on December 1st, in order to take care of the usual 行政手続き to set myself up. At this point, I am still technically employed by the US branch, but I immediately start doing paperwork, notably registering an address (住民登録 using my parents home) and getting the マイナンバー. I do this in order to quickly set up a bank account and brokerage account, in order to transfer my assets.

On December 15th, I start my official employment in Japan under the Japanese branch. Around this time, hopefully I will have a Japanese bank account and also begun transferring my financial assets.

In this situation, can one argue that I became a 居住者 on December 15th, as opposed to the 1st?

My interest in this is because I want to know when my Japanese taxation begins on my salary.

I also have an RSU vest that coincides near the time of my move-date, and I'd rather start my residency post-vest, in order to remove the headache of calculating the taxation allocation ratios (between US, California, and Japan) on this particular vest.

PS: I could just be overthinking this and they wouldn't care that much about whether its the 1st or the 15th in my hypothetical, given its only a couple weeks.