Steamy Dreams
I hadn't given her a complete obsession (not yet) - just a crush.
As far as Tammy was concerned, she'd suddenly developed a crush on her best friend's younger brother, and she couldn't see any reason not to act on it (because, of course, I'd methodically removed those reasons).
The whole thing went down just like I'd hoped. And yes, that started with Tammy going down, just like I'd hoped. My balls felt like they were full to the point of bursting; I was so close to fucking my sister, to owning her: mind, body, and soul. So close, but showing almost superhuman levels of self-control.