What are the three best and diverse countries to visit in Asia for a month or so long trip in the modern era?

My sister and I are dreaming/planning on doing a trip around each continent when we're older and we have the bread for it, and the one we're most excited about as westerners is def an Asia trip. we're planning on doing about three countries for each continent, and I was wondering what you guys thought about which countries we should visit. its about a week or so for each country, for reference. we need specific help in identifying safer countries too, as for example we wouldn't just travel to Jordan despite the natural beauty because of the fact its in the middle of a warzone right now. additionally, its better if the countries aren't too similar in terms of geography and food.

the only one that's basically a lock is Japan for the culture, food and hiking, but for everything else we're a bit stuck. I like the idea of Thailand and South Korea, but I don't want to drag the "southeast asian coast" feel too much, which is why I also like the idea of Oman too for the landscapes and culture. if any of you guys have personal stories or references to advocate for specific countries