Yep, we are related, whether through law or blood doesn't matter, all that counts is that things would be considered taboo by most other people! Our characters aren't quite familiar with each other in the beginning of the roleplay and it's more of a story in which half-siblings meet again after being split for most of their lives, or alternatively a story of two families merging into one and chaos breaks out between their children! Definitely seeming like the more popular one, just by appearance alone, she lovingly dubbed her new brother with the nickname "dweeb", seeing how he sits in front of his computer most of the time and rarely goes outside with friends. The brother on the other hand is quite flustered, being introduced to his pretty sister and things don't take too long for him to escalate!

Thoughts of the new girl sharing his space creep into his head every so often and soon he finds himself succumb to his fantasies, sneaking into the bath or her bedroom whenever he gets the chance, in order to get a hold of her underwear, furiously rubbing away while thinking about her big chest, full ass and elusive pussy. Always having fapped in the shower or on the toilet though, he never learned about how obvious dried cum appears and feels on fabric and so it didn't take long before his sister noticed what he was up to while she was not at home... gross, but kinda cute? Well, wearing those used pieces of underwear wouldn't hurt anyone and the kinkieness of it all feels quite unique compared to whatever things you've done before!

Maybe escalating from there, one day the sister decides to bust the bro in the act and a relationship of non-penetrative sex ensues. At first the sister would be taking over the role of the responsible sibling, making up all the rules for the relationship. "Putting it inside me? Sorry bro, but that would be seriously nasty. Too bad, to be honest."

Of course that's only an excuse to toy with him, trying to see how long he can hold it before taking what he wants!

She can invite some guys over and screw them and might happen to find a gap in her door ajar as the brother watches discreetly. Maybe she fucks his friends and they talk to him about how good she is, show him videos and photos they took during of her.

Thinking the sister is more a cool girl vibe. You know, does weed, hangs out with the skater boys, promiscuous and having fun, strong dislike for the orderly types.

This could even involve her new step father as well potentially.

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Quite open to this idea and the many ways it could go.

Preference is to use discord and/or google docs.

Feel free to look at other ideas in my post history