That's true, but in this game I still kind of view it that way. Mars is the true protagonist, but Erin is your more typical "protag" in the sense of the world they're in. The chosen hero with a hot mom, and two women in his close orbit. In his eyes, (the eyes of the more conventional protagonist), Mars is the antagonist. Even Mars has trouble morally, because he knows many of his actions are the actions of an antagonist. Erin is the would-be protag unlucky enough to be created in a netori game.
As for Mars dark skin, tbh I didn't think too hard about it at first, seeing as its a trope in the netori/netorare genre where the playboy girl-stealers have tan/brown skin. Trope or not, I do enjoy it tho, and hope it remains in game (which appears to be the case).