I've just mastered the Hiragana, and I know some signs for Katakana as well.
A while ago I opened up the Japanese version of Final Fantasy 4, and while I didn't understand much at all, I still think I could pick up some words.
This would in theory allow me to learn words and successfully build up my vocabulary; if one word sounds a bit similar to English, I can guess what it means, and understand the rest of the sentence better.
And so on.
I managed to pick up the words "heishi", "hikuteigan", "yoshi", "suuin" and "ankokukishi"; and Cecil was obviously named "Seshiru".
I actually think this is a little bit like moving over to Japan.
If you're ambitious enough, I think it's possible to pick up words here and there and improve your skills.