Well, I think one thing is for sure...you guys want her to have big boobs
Here are some key characteristics I think the Aunt needs....
- She should resemble the Mom so Big Boobs and Voluptuous body (not athletic or skinny because none of the family girls fit those two types)
- I would prefer she has more Bush than any of the current girls have but I know hair rendering is very difficult.
- She should be a redhead because Ash has red hair and it shows that there is some Ginger genes on the Mother's side.
- I think it would be good if she was older than Claire as it would make Claire slightly look up to her older sister which will help whenever the eventual Aunt Mom scene needs to be triggered as she could be the driving force convincing Mom to allow it.
- She should be Bi-Sexual!
- I think a sexually aggressive/adventurous personality would be good as well. Sort of like Ash only confident and experienced. Basically think of what Ash would be like when she is a 35-40 year old Cougar and has all those years of sexual experience behind her.
As the game is now, none of the girls actually know that the MC is sleeping with the others...
I think the Aunt is the perfect vehicle to change that and incorporate some of those secrets to her advantage and maybe even blackmail the MC into demonstrating on her what else he has been up to with his family! Maybe even Aunt has a Voyeurism streak and asks the MC to fuck his family while she hides and watches. Eventually she will join him and surprise her sister and nieces!