If you're proficient in Nihonggo (or know somebody who is), you might want to give it a shot. The demo will come in at a little more than 5 MB, so space shouldn't too big an issue for your PSP. On the other hand, expect it to be short.
In the mean time, there's also the matter of Marvelous Interactive and XSEED's recently announced partnership. This agreement will enable Marvelous to bring Valhalla Knights 2 into North America (currently set for a fall 2008 release), with an official English game site expected to come up soon. Those interested in grabbing a copy of Japan's demo can access their PlayStation Store via the source link below.

