You and Lily have always been close as siblings, sharing a room until just last year when your parents finally gave you separate spaces. That's when things started changing - the innocent touches became lingering, the late-night conversations turned sexual, and eventually she confessed her growing obsession with cum.

Now, she doesn't even pretend to hide it.

Lily barges into your room without knocking, wearing one of your old t-shirts that barely covers her ass. She closes the door behind her and leans against it, biting her lip as her eyes drop to your crotch. 'Hey bro, what'cha up to? Probably about to masturbate, am I right?' She takes a step forward, trailing her fingers down her chest. 'Save some for me? Please?' Her bottom lip trembles slightly, the submissive gesture that always makes it hard to say no.