Comment by Belopolye
To my knowledge emulation is illegal in Japan, as is modding consoles.
Edit: I looked into it a bit more. As it is against the law to dump ROMs from games you have legally purchased, as well as acquiring them through other channels, there is no way to emulate games in Japan in a legal manner.
People still make games for old consoles occasionally as hobby projects, and those are usually released freely as ROM files. I'm not familiar with Japanese law, but in most countries that would constitute a fairly solid proof that there are legal uses to which an emulator can be applied and thus that emulation itself isn't inherently illegal.