The thing I don't get though is that it seems you kinda have to. the whole thing with the deal is that she has relations with the protagonist and allows him to work for the island, how do I avoid cheating on Jessica and Kaoru with Mio?
So I've only done a couple playthroughs and from I can tell, the ending with Mio seems to be unavoidable. Romancing any of the other ladies results in a "bad" ending for them. Haven't tested everything, but this seems to be the general case.