What is the lore reason behind the EP world eventually affecting the real world?
The funny thing about these games is that they're pretty light on text, so the first best answer is we don't know. The second best guess is that it happens as a consequence of your actions in the previous games and this one. You get further corrupted, spend EP to corrupt others, and distort the EP world, eventually changing the real one. The interesting thing about how these games unfold and get more degenerate as they go on is that it implies you're almost teaching the EP world, something that's naturally pretty hostile to human life, to be lewd, especially in the second game, EP Girl. In these last two, though, you're more of a victim.
Sometimes though, you get those instant death sections with the weird orb thingies. I interpret those as the EP world going mask-off - that's what it
really looks like under the surface, when not under human influence.
Apologies if this interpretation is contradicted in the series or by the author - I haven't 100% completed all of them yet.