Dan brought Charlotte's sock to his nose and inhaled deeply. The socks had been thoroughly soaked in sweat, and their scent was strong. His erection stiffened in the air of the living room as he cupped both socks in his hands. Reaching down, he slipped one onto his fully erect penis while bringing the other to his nose again.
The feeling of her sock was luxurious as the silken fabric rubbed against him, delicately taut against him. Picking up her white sneaker, he stuck his socked cock inside of it, thrusting roughly, the sock allowing him to thrust just as well as a lubricant would. Her shoes felt tight against his dick, the ends pressing around him as if they were made to be fucked.
Stoked by the scent and feeling, his arousal was immense, and soon he orgasmed, ejaculating through the sock into the shoe. He wiped the cum up with the sock, spreading it over the shoe in the process. His semen smelled nearly as strong as her sweat, and they combined to form an intensely erotic scent. Not wanting to leave her single shoe like that, he decided to cum in the other one, too.
Grabbing the other sock, he put it back on his penis and began to fuck the other shoe. Raising the cum-soaked sock to his face, he noticed that his semen had reeactivated her sweat, making it smell even stronger than before, albeit coexisting with the smell of his cum. He fucked the shoe harder than the last, his arousal diminished but with more purpose, and he found the idea sexy anyway. He came soon after, dumping his load theough her sock into her cute sneaker. Removing it, he wiped the cum around the shoe and onto the sock, filling them with the strong smell of his cum.
By now, he realised that it was too late to turn back, and that he would have to live with having sexual relations with his sister for the foreseeable future. His arousal had entirely removed his inhibitions, however, so he found it easily to stop worrying and actually enjoy their newfound relationship.
Standing up, he realised that he felt better than he had mere minutes before, but noticeably more tired from ejaculating. Advancing down the hall, he pounded on their bedroom door, demanding entry.
After a moment, Charlotte answered his summons, and opened the door hesitantly. Dan barged into the room, practically shoving her aside, and sat on the bed, setting her soiled socks and shoes on the floor at the foot of the bed.
Charlotte sat on the bed next to him, looking sadder than she almost ever did. "Charlie, we need to talk," Dan stated matter of factly. She nodded solemnly, waiting for him to continue. "If we're going to have sex, it needs to be on my terms." She seemed surprised that he was still willing to have sex with her.
"Which terms are those?" she asked.
"Each of us can use the other whenever we want, but it can't detract from our relationship." Charlotte thought for a moment before accepting. Satisfied with the conclusion, Dan left the room, and Charlotte followed him.
Since they had both just masturbated several times, neither made a move on the other, and they spent the day hanging out with each other. At night, Dan wrapped his arms around his sister and cuddled her intimately without objection.
He woke up to find Charlotte pulling his pants and undergarments down. He sat up, but didn't object. Once they were removed, she stared at his erect dick in apparent awe of its size and appearance.
Dan got up from the bed to go the restroom, and headed back quickly after urinating. His penis was still erect, and Charlotte wrapped her small, soft hand around it as he sat back down. Pleasure jolted through his spine at the touch, at he thrust into her involuntarily. Smiling, she began to stroke his cock, her fingers stroking the glans gingerly but intensely.