Most good Japanese fighters seem to be afraid or something about fighting out of japan (dunno if there is another thing involved like honor, money or else beyond this, is something I really would like to know). A few with guts do and/or did it sometimes like Ryota Murata (Takashi Miura) and some rare old ones like Toshiaki Nishioka, Joichiro Tatsuyoshi and Kuniaki Shibata.
IMO a good confident boxer fights everywhere, it makes good to expose itself to this kind of different contingencies, environment and pression (the most u learn how to feel ok with it), most of boxers with balls go to japan to fight them (mostly Philippines, Mexico, thailandese) never (or very rarely) the contrary, just pick randomly some good boxer from Japan and see their career resume where the fights were done.
You see guys in active like the great undefeated Shinsuke Yamanaka and also undefeated rising stars Naoya Inoue and Masayoshi Nakatani (counting Hiroki Okada). I think you'll only see if they are what they seem to be when fight outside Japan.
* I can be divagating since this happens in US and other countries too, (I'm not saying all fighters you know) what I wanna say is that the great boxers capable of going outside to face others should do it, not depending on the house always. You see, for example, Mexican, Argentine and some European boxers, they go outside to fight regardless of fighting at home and many aren't too good or famous...
