Rape is justified for its inclusion in the story, as long as it's taken seriously, and used to further the plot in a dark way. Not some creepy fanservice like how Rance does it. Alicesoft isn't that bad though. From what I can tell about Nacha, there's no fanservice intended, (and is portrayed as how it is, inhuman, and horribly disgusting. It kinda helps that you play as a demon of cardinal hunger and lust, so your not some punk ass kid in look of "conquest", and quite rare that Hatsune makes victims of both genders, which is a rare case of female on male rape.)