Employer Refused to Accept Part-Time Resignation, Advice?

Hi everyone, I am having a dispute over my current part time job and I was wondering if anyone can chip in regarding the legal repercussion on this. I tried searching beforehand but I couldn’t find any that discuss this over part-time ([found similar one but for full-time](https://www.reddit.com/r/japanlife/comments/y3qqm7/employer_saying_she_wont_accept_my_resignation/)).

I am currently staying in Japan under student visa on Japanese Language School. over a month ago I was looking for a part time job, and Japanese person (let’s call him X) I happened to befriend 5+ years ago through some professional channel reached out to me asking if I want to do part time job in his startup in Tokyo (it was a remote work). I am not sure what his position is but somewhere along C-level. He also doesn’t live in Japan currently and managing the company remotely.

After some talk over the phone he mentioned to me about hour-wage, company condition, etc. (all in Japanese). I also conveyed my situation that I was in process of interviews with several companies for a full time position. On the WA message he wrote “掛け持ちしないで頼む” which I understood it as “don’t hold several positions at the same time” which I obeyed too, this was my only part-time job.

Last week I finally received an offer from one of the company and I have signed it. Because the start date will be early December, as soon after that I contacted X about my situation (I asked permission to speak in English to ensure I didn’t misspoke any word) and I wanted to quit my part-time position while also: 1) giving some tentative last date to ensure smooth project hand-over and stuff, 2) nominate one of my other acquaintance that can help to replace me for this work.

As soon as I finished, X berated me in non-stop Japanese, but in summary, “This is a shock to me, don’t you think it is strange in societal life? I have setup everything for you, insurance, pension, contract, project schedule etc. You wasted my time and my CTO time. You betrayed my trust, I don’t want to talk to you anymore. Now I have to do everything again from beginning. I don’t even need your replacement. What is even your motivation to work? Money? Experience? I don’t want to acknowledge this, you have to take responsibility! You will ruin the project timeline!”

At that time I was shocked and what flew in my mind was to de-escalate the situation. I said sorry and sorry and sorry, I didn’t mean to betray him, I already told my situation at the beginning and so, and because I thought of the company I offered some end date and replacement. But still he went on and on.

After a while X calmed down and ask me, “Do you know why I am angry with you?” and I said “Because you have high expectation to me to join your company” and he said no, he said “because you lied to me. One of the condition I gave to issue the contract was you have to drop out of all applications from all other company. I told you in the beginning and you said yes”. I was positive he didn’t said that and X said, “I did say in Japanese. Maybe you didn’t understand the Japanese but you should have asked me to repeat in English”.

This clause was actually not written anywhere in the contract. I checked it before and translate the word to English. Furthermore, because the part-time contract period was until January 2023, I even asked in chat what happens if I need to quit midway and he replied “there is a termination procedure for that so don’t worry”. I have a screenshot of this conversation. Had I know he expected such condition I would not sign the contract.

Now after that I went to discuss with my senior friend and the school. Both sides agree that this was close to ブラック企業 practice. Under no circumstance the employer might sue me or hold me against my will because no written agreement on that clause and I could just walk away. And generally I am not even a fulltime, just a part-timer; X’s expectation is misplaced.

I want to ask for your opinion on this:

1. Will this dispute stains my background record in any way in Japan for future employment/other stuff (PR application, etc.)?
2. Will this dispute jeopardize the offer I have signed for my full-time job? We have started the onboarding process.
3. Is there any legal repercussion I have to be concerned about?
4. It is very likely X will hold my part-time salary and refused to pay me in full or at all (I haven’t gotten any pay at all). Another story of this: X and HR apparently has different process for reporting work hour, I just found this out yesterday. All this time X told me to just created a spreadsheet to log my time, but HR actually requires me to submit in their own template of Excel. HR then told me to send to X, cc HR. But X soon replies in the email thread “I will check for this first, please wait for final version HR” then quickly chat me “. I read that I could report to Labor Bureau for this but will that be effective on this case as the person is not in Japan and the company itself might not know about this feud.
5. Do I really required to put notice period upon quitting my part time in this situation? It is not mentioned anywhere in the contract as well, and after I processed his tantrum I was getting the sense he was controlling and I wish to not working any longer with him ASAP. I am thinking on quitting right. I happen to know the Japan labor law recommends 14 days of notice period.
6. One of the process I had to do for this part time job was, there was some year end tax adjustment (年末調整) that I had to do over freee platform. I submitted MyNumber card photo on it, guided by HR. Anything I should be concerned about this?
7. Any document/proof I had to obtain from the company before ending my part time?

I am sorry I asked a lot of questions on this, I really appreciate the collective thoughts of this sub and thank you in advance for your reply. I am also in process of thorough discussion with my Japanese school and are going to consult with FRESC/FRESC Houterasu.