His sister.

"Adam, stop jerking it and get ready for school, Mom already left for work!" Adam's sister Sarah yells from behind the door. Hearing no reply she opens the door saying "I thought I told you to quit beating off and get your ass ready?" Seeing Adam in bed she asks "Are you sick?" But instead of reaching to feel his forehead she straddles his waist and grabs both of his hands feeling that one of them is warmer than the other Sarah says. "Quit trying to fake being sick and get the fuck out of bed." While she climbs off her brother and pulls the blankets off him. Sarah looks at her naked brother he seems a little smaller than she remembers him being, when she sees between his legs she says "Pretending to be sick so you can stay home and use a pocket pussy? You are just the lowest of the low." As she reaches to take the "pocket pussy" off to further mock him she gasps as she feels the heat and size of his cock. She gives it a little tug, still trying to take it off, but all that happens is her brothers monolithic slab of manmeat twitches in her palm. "This can't be real." Sarah mutters, "This isn't real right Adam?" Sarah asks her voice quivering slightly, her eyes unfocused as she gazes up at him around his shaft. "Oh, it's real Sarah, so would you mind telling me why you're still stroking my cock? Don't tell me my perfect cheerleader sister is actually the perfect incestual slut?" "No, I just thought your little dick was cute," she says her eye's glassy, staring at Adams phallus as she absent mindedly strokes it. "and although I might haved jilled a few times smelling the cum stains in your underwear, it was only because I knew they were there because I'd been teasing you." Sarah lick her lips her eyes focusing on the cock before her as she strokes it with purpose now. "But now the cock of my dreams is attached to my cute little brother, it's like those two things mirged into one fantasy, and all I can think about it making my cute little brother's big manly dick cum." Adam sees the hunger in his sister's eyes as she focuses on the bead of precum oozing from the tip. But then Sarah suddenly stops stroking him. "Wait right here baby brother," she says with a wicked grin. "I'll be right back."