How do you become a wrestler in Japan? -

Because when people say that a wrestler/diva has wrestling experience in Japan, it usually means that they re a good wrestler.

Like a sumo wrestler?

Eat a lot of hamburgers.

you need to be a good wrestler

Well first you will need to find a trainer. Someone to help mold and guide you. From there focus on getting into NJPW or Dragon Gate, both are great wrestling promotions. Good Luck.