I've read this three times but it never gets old, seriously. (Nothing beats In the Palm of my Hands but anyway, continuing with what I was supossed to be saying instead of side comments) It is based in the ninja world and not an AU.
It's also based on the timeline where Sasuke returned to Konoha for good. Warning though, it contains mature contents, again. But it has a good plot and you wouldn't regret reading it.
So.... you know my ending line. Enjoy reading it. It's worth it.