70% PS5
30% Xbox

I thought about this, that Xbox will gain market share, purely because

a) The console market shrinking
b) PS5 is very large and Japan does not like big gadgets,
c) Xbox share is minuscule and the only way from there is UP;

However, I decided to not go in that direction in my estimates because

a) Japan console market is shrinking and its effects globally are increasingly smaller,
b) Even if people swing in favor of Xbox, it will be a minor one; XBS will DEFINITELY sell way less than X360 (1.65 mil), and more than XB1 (110+ K).

My best bet is that XBS will sell less than a million in Japan, and in the overall scheme of things, assuming a sales equivalence with the 8th generation, whether XBS sells 54 or 55 million hardly makes a difference. So I decided to keep the formula for swinging factor unchanged for Japan (which is negligible but positive). I am pretty sure, there will be several sub-regional deviations in my estimates but in the grand scheme of things, things tend to cancel each other out, and smooth things over.

Well technically yes, it will gain market share, but in realistic numbers, it hardly matters. In my analysis, it suggests a 0.01% increase in market share (from 1.40% to 1.41%). However, this is just analytics. In reality the increase might be much larger since the market share is too tiny to begin with. In any case, X360 levels are a dream for XBS, which will be somewhat greater than XB1 levels.

Those who say that Xbox will win some marketshare in Japan are right though. It's not optimism, it's common sense. You know how they'll do it. Even in worst case scenario, that you mention - if they just sell 75k. Okay, that's just around 30-40k loss compared to what they have this gen. But PS5 is very likely to sell a couple millions less than PS4 did. And that's where marketshare gain comes for Xbox. If you lose way less than your rival, you get some marketshare back

I think people are underestimating Ps5 and Overestimating X Series S/X.

Here in Australia as an example, two weeks before launch there are still plenty of X Series S stock.
PS5 Normal/Digital is sold out until mid/late 2021 and whilst Series X went sold out after a few hours, there are some “reports” claiming that there were around 500 PS5 units allocated in each EB Games Store against around 25-30 Series X.

Obviously this has to be taken with a grain of salt.

Good analysis, clearly you have done allot of thinking and gathering of information to formulate your predictions and spent the time and effort to showcase that.

pretty much.

The only way the ps5 sells as much as the ps4 in japan is if they pull out ALL the stops to make it appealing to japan, which i don't see them doing as japanese market trends are opposite to what appealing to the mainstream west is.

and plus, ps4 honestly won by default last gen.

I would say its more to do with the censorship craazy Sony is going with. The japanesse hate that shit and it definetly shows in their purchasing habits. Be it games, anime and what ever else. 

It's also very huge, way bigger than even original Xbox which size is always being brought up as one of the reasons why it didn't do well in Japan.

and the ps5 is set to be bigger.... yay.

plus japan no care that much about 4k, when you have a small apartment where a 4k tv is overkill whats the point.