Okay, what Degee(s) do I need to become an ESL teacher in Japan?

[Glenski]

Amity. They are a part of the eikaiwa organization called AEON, one of the 3 largest in Japan. Amity specialized in kids, if I recall. A handful of these eikaiwa do what you wrote. No surprise.
www.aeonet.com

Other similar groups:
GEOS
the former NOVA (now owned by G-COM)
ECC

 

[kusojiji]

I mean, I want to move to Japan young, not in my thirties.

.............................ouch!

 

[Akakubisan]

Many community college's in the US now offer various 4 year degrees from there campuses. These are usually through connections/agreements with a certified university that actually gives the diploma, but without the need to go to that school directly.
This has become much more common in the past 10 years.
This is usually through dual enrollment. see here Home as an example.