The character on the left, why does she have to look like that when you can also make a few 'improvements'? You said you are not familiar with the 'hentai game world', so I'll give you an example for some inspiration.
I have attached some Images; Evil Lady's hairstyle would have to be similar to Image 1 and 4 put together (how you do it is your choice, you can look up 'anime female hairstyles' for more ideas), her face would be similar to Image 2, 3 and 5. Her body's appearance can be based on Image 1 or 2 to give her that evil sexy look that matches her age, and her skin doesn't have to be green because accentuating her other traits such as facial expressions, personality, and voice acting in an h-game fashion can more than make up for it. Also her bust size would have to be bigger (Image 1, 2 and 5) than the other princesses. And lastly her horns can be the one on Image 6 but black and facing backwards.
Speaking of voice acting; I frowned a bit when I heard the characters talk, try to remove the uptalk tone and valley girl accent/dialect (e.g. 'like,','so' and 'I mean', the usual words the valley girl accent typically use) when working on the game further, the guy who voiced the Narrator is fine. The VAs on japanese games and anime - hentai or not - may not be understandable due to having a different language but at least their tone is not bad, at least for me. The voice acting doesn't have to be a highly professional one, just with enough skills put in so those playing your game don't mind it. And just in case if the VAing didn't work include an option to disable voice acting in the settings menu (Except for the Narrator guy, he's cool).
Edit: Re: her skin doesn't have to be green
Since she lives on dark and cold places her skintone would be of a pale cold winter white instead of the warm spring white of her 'foe' or the Girl on the Right in your picture.
