A few notes for those who don't know how to do this:
To set up a Japanese PSN account, watch this and follow the instructions:
http://www.youtube.com/watch?v=Qta093zW5eMThere's some other tutorials out there as well or you can always make one in your browser and either use your knowledge of Japanese or a web translator (they work well enough to get the point across).
If you're interested Devilotmarkky's idea, you're looking for "Angel Senki." Go to where it says "PS3" and look around until you find, as stated in earlier post, "エンジェル戦記".
http://www.angelsenki.jp/guidance/index.html

Also, if you want to actually buy some games like, say, FFVIII (since it just came out and isn't up on the american PSN yet), go to eBay and, for the most results, type in "x000 yen playstation" (substitute x with 1, 3, 5, or 10). The prices are a bit jacked up for convenience and profit reasons (i.e. a 3000 yen [$33 roughly at the current rate] will cost at least $40 from most sellers) but it is great to find unique games and test your Japanese skills thus far.
Most of the sellers will just e-mail you codes and you input them in the store. I've only used one seller, extreme_samourai, and they are VERY good and very quick. Got my code about an hour or two after placing the order.
Now, as for being able to type within Angel Senki, you'll want to set your language settings to Japanese. To do this, do the following:
- Go to the second left tab, "Settings."
- Go four spaces down to the cube. This should be system settings.
- The second option within that is the system language. Change this to Japanese.
- The third is character input option. Change this to Japanese as well.
You can go back and easily change these whenever you need to, but I think that the whole thing is easy enough to navigate.
Why do this? It allows you to use Japanese characters when conversing so you can maintain a conversation with other Japanese players. Also, for your convenience, in the input box, you can easily switch from Japanese characters to Roman ones in a snap, so if you know your PS3 menus pretty good, you might not need to switch back!
If you want to add me, my PSN is TerraAshura.
P.S. If you purchase Final Fantasy VII International from the Japanese PSN store I am trying to get a project of my own going to translate the game and keeping together a side-by-side script. If it's still a bit foggy, here's an example. Have you ever had to read a Shakespearean play in school and the left page was in Old English and the right one was Modern English? Same concept.
Anyone interested, go here:
FFVII Translation Project