It's a gaming laptop. I am absolutely not kidding when I say these things are like the mythical phoenix, consumed by the very fires that gave birth to them or high performance cars where just driving them is akin to abuse. Even setting aside all the other reasons why laptops make for a horrible gaming platform, the biggest one by far and away is the lack of ventilation.
Most laptop cases are made of plastic because it's cheap. Problem is, plastic is a terrible conductor of heat, so by the time plastic even feels warm to the touch, it's probably at least 2-3X warmer on the other side. Combine that with the tight confines of the case and the fact that it sounds like you only have one fan in this unit and you can see that this thing was designed to last only as long as the warranty.
Proper airflow is one of those things that seems very simple but is not. Ask almost any engineer and they will probably groan if you mention a fluid dynamics class, sort of like med students with organic chemistry. Despite air being a gas, it moves like a liquid for the purposes of convection based cooling. Most laptop makers, even Apple, only have exhaust fans, but if we remember Newton's Third Law of Motion, every action has an opposite but equal reaction. So for every cubic centimeter of air that is expelled from the case, a cubic centimeter of air has to be pulled in to replace it. That's where the cooling of most laptops breaks down. Instead of having one fan forever pulling IN cool air and one fan forever pushing hot air OUT, creating a constant stream of air flowing through the unit, they just push the hot air out and rely on the resulting difference in pressure to create enough of a vacuum to pull in more cool air. If you were to take something like dry ice gas and flood it into a laptop so you could see what happened, you'd see that the fan (typically mounted on one side or the other) has a limited area of effect and you have this big pocket of air on the opposite side that tends to just sit there.
In most laptops I've ever worked on, the heatsink snakes around and ends in a grille-like appendage which is right by the fan. So, the idea is that the heat from the CPU is drawn into the heatsink and carried along this metal conductor where the fan is providing a lot of convection cooling. Some of the heat will bleed off into the rest of the case and I'm still not seeing you mentioning anything other than CPU temps, when you also have to be concerned about the GPU. Those are just the major heat producers however, your problem could be caused by the 2 years worth of slow baking that the rest of the circuitry on the motherboard has been subjected to. Solder joints have likely become very brittle and some may well have cracked causing intermittent cold solder joints based on the thermal expansion/contraction of the unit.
The application of little more than a high school level understanding of physics would go a very long ways to helping understand what is likely going on. It'd also help people avoid buying a great many useless trinkets and solve a great many problems that maybe they haven't encountered before. However, you can basically sum it up in this case as: Gaming laptops very rarely survive more than 18 months without needing major repairs. You've gotten around 2 years out of yours before issues started manifesting, so count your lucky stars and next time get a desktop if you want to play PC games or just understand that you are unlikely to be so lucky a second time with a gaming laptop. Since you live in Japan, maybe consider a game console. Especially if you're an RPG fan. Japan is like nirvana for the JRPG fan since for every title that gets released in the US there's 2-3 that never make it out of Japan. You can also get the titles at least 6 months earlier and people swear up and down that Japanese voice actors are better than their American counterparts. So if you can speak/read Japanese reasonably well, that will keep you pretty well occupied.