What if Rin ended up as the evil one instead of Obito?
There aren't many really impressive evil women in Naruto, Kishi sucks at writing female characters in general, "love makes you evil" is kinda cliché, Rin is a sweet girl but I'm interested in seeing it it's possible to make her something other than a martyr/saint. Especially since Obito basically regarded her as the paragon of goodness and blahblahblah.
Rin's confused feelings about Obito's feelings towards her results in a strange sort of fixation/obsession after he dies. She's not sure if she loves him, or if she wants to love him, or if she even wants to be loved by him at all since he's DEAD. Seeing Kakashi's immense guilt over all that happened only puts her in more emotional turmoil - why did this have to happen, why doesn't she know what to feel, why is the truth about the world she lives in so horrible, etc.
She starts feeling like she owes Obito way too much but has no way to pay any of it back. The question of "Why did everything have to go wrong?" keeps spinning around in her mind, and then something else happens - maybe she gets captured by Kiri again because Madara wants to push Obito over the edge, but things go crazy and Obito dies, again, in order to keep her safe. (And possibly gives her his remaining eye?) That's when she decides that's it, fuck this, fuck everything, she's going to remake the world so they can redo everything and make it go right this time. Because she believes that Obito deserved better and she's tired of being tossed around like a pawn or a weapon or a toy - first she gets captured by Iwa for information, then by Kiri for attacking Konoha, then some weird plantmen show up and try to capture her as well.
Screw that, she'll get power of her own - she does have a bijuu and a Sharingan at the moment after all - and go fix everything that went wrong. Later on the plantmen approach her again with a proposition from someone claiming to be Uchiha Madara, and she accepts because it doesn't matter how she gets the power or where she gets it from as long as she reaches her goal.
(Kakashi is going to end up in so much angst as a result of all this. He feels obliged to protect Rin but she's nowhere to be found and when the two remaining members of Team Minato finally meet again it's on opposite sides of the battlefield. Caught between his duty to his village and the promise he made to his dead teammate, there really is no right answer... or even an answer at all.)