So i've been mainly playing live poker in Iowa as a college student but I decided to go back to Japan while finishing my degree online. I dropped out couple years ago and I've been working in some stupid sales job but decided to go back to Japan since I haven't been there since 4.

As I spend 2 more years finishing my degree online, I realized that it is a perfect time for myself to keep working on my game but in Japan there are no casinos.

Obviously anybody can play online poker but since it is illegal in Japan, I wonder what poker players do when they are in a country where poker is illegal.
-Do they just go to online pokersites like 888, betonline, unibet?
-What do they do with taxes?
-Do they fly around playing tournaments?

I don't know the exact T&C of every poker site but I would assume you will keep your residency in Iowa, and might even already have a few accounts at the various sites that are allowed in the US, with that being said possibly look at a VPN and use the US as a gateway? That to me would be the easiest solution, however read the T&C at each site, and use your judgement if it falls under a gray area (not mentioned).

There are some (legal) poker clubs in Japan where they play for prizes/points, not cash. But your best bet is going to be playing online. Pokerstars services Japan, as do a bunch of other major sites.