The first thing that you need to look at, unless you already have it, is the Class 1 medical. It's quite a bit more in-depth than a Class 2 (or equivalent), things which aren't a problem for a Class 2 can entail referrals or unfitness for a Class 1.
Secondly, as far as I'm aware, Japan prohibits dual-nationality, so working abroad may be somewhat limited due to being unable to get a second passport. That said, carriers have occasionally run international cadet programmes, Cathay Pacific and one of the ME3 have done so in the past. Singapore Airlines has a programme which I believe is open to foreigners but they prefer locals, it might be worth a look.
Beyond that, it's really a case of saving up and paying for training, it took me years before I started modular training in the UK. I don't know what flying schools in Japan offer commercial licensing, or which training schools overseas offer the opportunity to get a Japanese licence. Airline Pilot Central might have more information if you want to train in the US.