PHANTASY STAR UNIVERSE is suppose to be an online and offline game both are going to be different style of games.
But as your average RPG has four to five discs to play on them will PSU
offline game have that many discs to play with AND the online disc to play the MMORPGP part of the game?
Your thoughts.
Either you’ve been stuck in the 90’s, or you’re talking about a PC SKU or something…
Four of five disc comment aside… if PSU is both online and off (I don’t remember any recent news about it saying anything either way), there’s no reason it has to be on separate discs. Phantasy Star Online worked online/offline using one disc just fine.
If you seen the trailer that’s where it states the question if it’s PSO 2 or PSV
and with the reports that it could be both a proper offline adventure different to the online one I can’t see that happening if it shared the same disc. PSO was limited in it’s offline adventure compared when it was online.
We now use DVDs and I don’t think any game out there has been four or five DVDs… 
I’ve seen the trailer. But there hasn’t been any official information since the trailer–just a lot of speculation. Even the advertising text says “Phantasy Star V” and “Phantasy Star Online 2?” with question marks, as though the new game could possibly be those or nothing related to them at all. It’s not saying that the game is both. It’s not saying that it will be one or the other. It’s postulating that it could be, but you really don’t know. Until more details surface I think it’s premature to worry over how online/offline play impact each other (if it even has both modes at all!).
But if the two modes both exist on the same game, I doubt that would be cause for two separate discs. If online and offline play are so different from each other that they can’t share the same disc, they would essentially be two separate games and Sega would sell them as such.