Alright, so here's a quick rundown of how these things work.

Copyright is the inherent protection of any intellectual work as soon as it takes material form. There's no need to file any paperwork with anybody, though it is common enough to file the work with one of a number of organizations for the purposes of proving copyright if any cases do come up. This is simply to establish an unquestionable date that the copyright took effect by. Razgriz is a single word and not a fully formed intellectual work and as such does not qualify for protection under copyright law. You're safe there.

A trademark is a filed and purchased protection for words, phrases, and images that are uniquely and inextricably linked to a brand or product. Razgriz could conceivably be protected by trademark if it meets that qualification. Now, does it? An inquiry could take a while, but an easy way of finding out is to see if the word is in fact unique to Namco's Ace Combat or if it exists in any other form. I couldn't find anything that might constitute a pre-existing, non-referential use of the word so you very well might be in trouble there. However, I also didn't find any explicit trademark associated to Razgriz nor any reason to believe that it is trademarked.

Summary of findings: The concept of Razgriz as a whole is protected under the copyright by the protections offered to Ace Combat 5, but it seems unlikely that the word itself is protected in any way.