I have spent almost 6 months in Japan (entered country 16th of November and left 10th of May) am I going to need a police certificate from Japan for that period?
I am unable to answer the *specific* question on whether you will need one, but I have just had to get one (having lived in Japan for two years). In order to get a Police Certificate you need to show the police some documents that demonstrate you require one. For me, that involved showing two letters: one was that I had an offer of employment in Canada, which explains why I was trying to get a work permit in the first place, and another from IRCC specifically requesting the Police Certificate.
That is to say, until you get to the part of your application where you are requested to provide one, the police here in Japan are probably not going to give you the document. Therefore, I would factor in the possibility that you will have to get a Police Certificate, but you shouldn't worry about it until you receive the specific request.
Just for additional information on the procedure, this is the process I went though in Ibaraki prefecture (where you live might determine exactly what you're to do): I had to go to Ibaraki Police Headquarters taking with me the two documents I mentioned earlier, plus my residence card and my passport. They took some details and my fingerprints. They then told me that I could collect the document in approximately one week. In fact, I got it exactly one week later so it can be generated relatively quickly. You will also have to pick up the document as it's unlikely they would post it. If you can't speak Japanese (I can't) then it might help to be accompanied by someone who acts as your attorney (the very helpful administrator at my work assumed this role for me). If you don't have a suitable companion who can help, you might need to book a specific time slot rather than just turn up (presumably so they can ensure there are no problems in communication). You can return to collect the document in person, or sign a form that lets someone else with the power of attorney collect it for you.
