Yeah, dropping the "science" in the title is fine.

I'm not too familiar with Nanoha, and by virtua lRPG, do you mean like black mages from the final fantasy series, using elemental attacks?  I was thinking elements would probably work, where an element is tied to each sin.  Which sins would your two characters have?  Maybe the magic can be named after the Rias, like Riamancy or something.