Your brother is mean, bossy and rude. He is always hogging the tv so he can play video games while making you do whatever he wants. So, you decide to teach him a lesson. You bring him a bottle of water that has a very special ingredient in it. A serum that will turn him from a guy into a girl. Maybe once he's a girl, he will be nicer and less domineering. Or so you thought... You hear a shout from the living room. Your brother has woken up from a nap, but he is no longer your brother. He is now a girl! Your new sister yells at you, demanding to know why she woke up in this body. She knows you had something to do with it. After all, you're the only person who could have put her in a dress and put makeup on her. You can't help but let out a laugh, which infuriates her. She yells at you more before telling you something that you already know. Your plan didn't go quite like you thought it would. Instead of turning your brother into a complete female one part was left unchanged. Your sister still has her same huge cock. You now have a futa sister. A futa sister with a raging hard on. She pulls it out of her underwear and it sticks up in the air, bigger than any dick you have ever seen before. "You're the one who caused all this, so you're the one who is going to be taking care of this" your futa sis tells you, startling you. She then warns you that you better not think about running away. You better get down on your knees right away before she beats you down onto them. You listen and get down like she wants. She starts off by jerking her girl cock right above your face. Seeing her hand glide up and down her huge cock is stirring up some feelings within you. Feelings of intense arousal. This does not get past your sister and she meanly teases you. Even that serves to just turn you on further. You're practically eager to suck her cock. So, when she finally lays back and tells you to begin sucking her gigantic futa cock you do so without hesitation. The whole time she teases you. Not only that, but she tells you that you aren't allowed to touch your cock at all. And don't even think she is going to be fucking you in the ass. The only one who is getting pleasure will be her. Although, it does feel good having her huge girl cock fuck your throat as you bob your head up and down on it. When she gets close to cumming she kneels above you again. You're going to open your mouth up wide and you are going to take every single last drop of her cum and swallow it all down.