Asia recs!

I’m studying abroad in Tokyo for a semester, based near Haneda/Narita airports. Budget is roughly $800 per weekend trip (flights + hotel + activities) and $1,500–$2,500 for spring break.
Travel windows:
Regular weekends: Thursday evening – Sunday night (so realistically only about 2 full days on the ground once you subtract flight time on each end)

Spring break: 12 days in March

End of program: 7 extra days in June before I fly home

Where I want to go: Thailand, Vietnam, Jeju, Seoul, Taipei, Philippines, and I’m open to other Southeast/East Asia destinations that work well as a short-haul weekend trip from Tokyo.
What I love: nature (hiking, waterfalls, coastline), wellness (onsen, hot springs, spas, yoga), and adrenaline activities — think the Azores: hiking trails, waterfalls, beach time, and stuff like canyoning or diving. I loved how compact and nature-dense that trip felt, which is what I’m hoping to replicate on a smaller scale.
What I’m not into: museums, temple-hopping, or history-heavy itineraries — I’d rather spend limited time outdoors or doing something active than sightseeing indoors.
Specific questions:
For a Thu–Sun trip out of Tokyo, which of these destinations are actually realistic without losing a full day to transit on each end? (I’m guessing Jeju, Seoul, and Taipei are easy yeses, and Thailand/Vietnam/Philippines are tougher.)

Since I’ll likely be staying close to the arrival airport for short trips, what are the best nature/wellness/adrenaline spots within about 1–1.5 hours of major airports in these places — e.g., Jeju itself, Gimpo/Incheon-adjacent Seoul options, Taipei vs. Hualien, Chiang Mai vs. Bangkok, Danang vs. Hanoi?

Which destinations should I hold off on and save for the 12-day spring break or 7-day end-of-program trip instead of trying to cram into a weekend?

Would love any first-hand recommendations, especially for hot springs/onsen-style wellness spots, hiking trails, waterfalls, or adrenaline activities (diving, canyoning, etc.) near these airports. Thanks!