Genuine question - where is the white stuff coming from? Is it supposed to be a kind of mega-lactation, or is there some dude lurking in the background and wanking over the girls?
Having look up the game website, there seems to be an optional "mystery white liquid" button just after the girls climaxed. Think of it as a way the producers are allowing the players the break the 4th wall and join in on the fun. In some of the sample scenes' dialog, the characters even make mention of the stuff "Ahhh! Where's all this hot, white stuff coming from!?" LOL