Lol... Incest in the Sims...

It's true. I made myself a Kingdom Hearts family, and it went like this...
Axel and Kairi Leonheart (Siblings. Children of Squall Leonheart and Oerba Dia Vanille)
Riku and Namine Strife (Siblings. Children of Cloud Strife and Paine)
Vanitas and Xion Fair (Siblings. Children of Zack Fair and Oerba Yun Fang)

Now, what I did was this:
Xion marries Axel, so now she's Xion Leonheart.
Riku marries Vanitas, and now he's Riku Fair.
Namine marries Kairi, so now she's Namine Leonheart.

Xion and Axel have a kid, who's Roxas. Roxas grows up and marries Cornelia Goth (because Roxas is a homewrecker). Now, I go to send Namine to be happy for him, since it's a Namine-type-thing to do, and I find that she can have romantic interactions with her nephew.

Now, let's review the family tree, shall we?
Axel marries Xion who's brother is Vanitas who marries Riku who's sister is Namine who's married to Kairi who's brother is Axel who has Roxas with his wife Xion.
Brain hurt yet?
Therefore: Roxas is Axel's son, and Kairi is Axel's sister, which makes her Roxas' aunt. Kairi marries Namine, which makes Namine the aunt to Roxas by marriage, thus making her Roxas' aunt-in-law, in a sense.

And so, you can do incest in the Sims 3. Enjoy~

Lolbutseriouslythough. I find that funny. And I know it's not really incest, but it's like banging your second cousin. It's not REALLY incest, but it's still frowned upon by most.

Anyway, now I'm going to totally wreck the home. Should I have Roxas make the first move, or Namine? >X3