Idea, crossover with Code Geass:
Lelouch is reborn as the twin
sister of Sasuke, Lulu
P). Mikoto, his/her new mother has a personality similar to Milly's or maybe Kaguya (Sumeragi)'s, so hijinks ensue, especially when little Lulu gets her name legally changed to Luluushu
D). While interested in being a ninja, Lulu didn't put much effort into training her physical stamina or strength, beyond what 'her' mother and the Academy pushed onto 'her'.
Then Itachi killed everyone, and "Lulu's" little vacation from changing the world comes to an abrupt end. The Masked Man (Obito) easily danced around her during the massacre; she outsmarted him and nearly got him... except Lulu's body was far too slow and weak to take advantage, even with the (newly awakened) Sharingan.
Obito thought he killed her, but she has some regenerative capabilities (from a Code?). Still, it's not a full-fledged Code, so she most certainly can die. Lulu realizes that she needs to keep up physically, so she REALLY steps up her training.
She gets put on Team Seven in Sakura's place. (Yes, that's why Lulu's female!) BTW, she doesn't have her Geass, the Sharingan should be enough of a substitute if used cunningly. "Absolute Obedience" is way too OP for the Naruto world (I'm certain Lelouch would be able to control the Gedo Mazo, the full-fledged Juubi, Kaguya Otsutsuki, and any other Otsutsuki.)
I imagine that "Lulu" would be VERY protective of Sasuke, and would not think much of Naruto due to his lack of intellect. Or maybe 'she' would have a hard time reading the guy and think he was hiding his intelligence beneath a 'mask', only to discover that Naruto truly isn't all that smart, even beneath his mask. (Insert a "Take That" to certain Naruto fanon clichés.)
I'd imagine that this universe likes to mess with Lulu even more than 'her' original one did. From changing gender to getting a tease as a mother, to Shikaku Nara beating her at Shogi, to Shikamaru constantly hounding 'her' for rematches (which he can't win), to Naruto hounding her for any reason (maybe a crush?), to more serious stuff like the massacre and Orochimaru's plans.