See other submission for Alicia/Jules back story. This isn’t intended to be a serial, just exploiting a real situation; although details have been changed.
Alicia is going out with some friends today and is up and about at 6:30, she has her breakfast and her shower, and all the time Jules is watching her from the bed. He is playing with himself as he watches her, she knows that because she can see his hand moving surreptitiously under the duvet, although he thinks that she can’t see anything. He believes that if she had seen something she would say so, but he doesn’t know his sister as well as he thinks he does. In fact she is quite turned on by the fact that he is looking at her and getting horny, and the knowledge that he will wait until she leaves to make himself cum makes her feel a little pleasant sexual jealousy. She thinks about it in the shower, and is going to masturbate herself while she is in there but decides to give her brother something to think about instead and she knows that she will be better at that if she is still horny.