It seems to me that Japanese (more so than Korean but the Korean's do also seem to have this trait) have the inate ability to control their body temperature. I know it sounds strange but hear me out.
I was in Hokkaido for a week. Sapporo, Hakodate and Abashiri (which is SO cold!) in the middle of winter. Japan in winter is like Cairns in summer - everything is adapted accordingly, so you go into a shop or a hotel, or a home and everything is heated. If you venture out onto the street it's only for the absolute minimum of time you have to be there. It is bitterly cold and to go outside you need the proper equipment: we're talking jackets, parkas, gloves, hats, scarves, the works. You flat out can't go out without all the paraphernalia.
However... in Sapporo particularly, I noticed something very odd especially in the shopping centers. I was wandering around thinking how annoying it was to have to cart all this crap with me (jacket, gloves etc) and looked around for others doing the same thing. There was no-one else doing it though. It was just me. Huh??
All the Japanese people were still fully rigged up in their puffer jackets, gloves, knitted neck warmers and hats but they were inside the heated shopping centre. I started taking more notice and sure enough everywhere I went the Japanese would be inside for 30 or 40 minutes and still have all their winter gear on. I would have been cooking and at one stage tried keeping my parker on once I came in out of the snow. You know how long I lasted - about 3 minutes. These places are heated to probably 20-23 degrees and not a single Japanese person has taken off their coat. I saw girls with multiple bags which meant they had been there for possibly hours still wearing their puffers. How are they not a giant sweaty mess in there? No-one is though. Its bizarre but it got me thinking.
I know I have crap climate control and it does technically have a name which I can never remember, but basically I overcooked myself with a very bad fever once, and now my AC doesn't work so well. As long as its hot I'm OK but when it is cold I can get very warm very quickly if I'm rugged up and then the temperature increases so I'm very aware that I'm constantly putting layers on and pulling them off in cold weather. The Japanese however seem to have entirely the opposite advantage. They can be outside in the freezing cold and be dressed for those conditions and then come inside to where its 20 degrees and not feel the effects of the warmer conditions.
I started noticing it everywhere I went and then I started looking out for other tourists and noticed that, like me, they shed when they came in out of the cold (pun unintended) however the Japanese just came in, ordered their coffee, lunch or drinks, sat down with their friends and proceeded to socialise in gear that was suitable for -5 conditions.
I never could make sense of it but it was if nothing else interesting...