@Huii
If you want a "soft impact" with Japanese, I'd go for an intuitive tactical game or a rhythm game. This way, you have some Japanese text and dialogues to sustain the story, but with obvious gameplay regardless of your language knowledge. I'd surely avoid visual novels, but also JRPGs, where you might have to fashion out what to do following obscure suggestions given in dialogues... Sadly, I don't know what kind of Vita JRPGs are safe or not, from this point of view.
@NesFe
I guess God Eater 2 Vita did really well through digital downloads. Luckily for all of us, it looks like Famitsu is going to publish digital sales charts every month, starting January 2014.
http://gamrconnect.vgchartz.com/thread.php?id=159902&page=534
Finally, Neptunia Noir graphics look adorable, but after playing some Disgaea I discovered that this kind of games are not for me...
