The Vegastrike universe seen from the real world
Vega Strike instances a fictional universe. Considering that Vega Strike is a game that simulates a world --- in the philosophical sense of that term --- makes obvious the difficulty of explaining the term 'universe' with regards to Vega Strike:
The explanation of 'universe' here is inevitably tautological, as it leads to say that 'universe' is something simulated by a game called, in this case, Vega Strike. Though one may figure that the 'universe' simulated by Vega Strike is fictional from the point of view of reality, the 'universe' in question does actually exist because Vega Strike does exist.
The Vega Strike universe exists. Thus, one should be able to describe it :)