This plot revolves around the Idea that Sakura grew up to be Genkai
What if Genkai was Sakura? They both have pink hair! And they have been saving their energy in condensed spots too. Maybe Toguro is Sasuke? He is obsessed with power.
During Naruto and Sasuke's absence, Tsunade trains Sakura's chakra control by having her use it to balance on a spike in the same way Genkai does to train Yuske. Naruto returns from his training first with Jiraya and then the toads. Sasuke succeeds in killing Itachi but remains power hungry. He returns to the village but only for the betterment of his own ability. People may be suspicious of him but they accept him because he killed Orochimaru. The three are then reunited and named the new Sennin. A wealthy feudal lord pays huge amounts of money to hire them. The mission he gives them is to compete in a tournament and win. He is betting on them. Naruto is furious at the idea of being nothing but a piece in a game of senseless violence for the entertainment for the rich. Sakura hates the idea too but realizes that they cannot back out on a mission that the village has chosen for them. It would ruin the leaf's reputation and would lose many clients. Sasuke is happy to fight. To him it is just an opportunity to test himself against the best and become even stronger. Naruto and Sakura are shocked at his willingness to cooperate, but still don't fully realize how he has changed until he asks to be made into a demon. They both try to stop him but eventually fail. Naruto dies dies in the resulting battle, killed by Sasuke. Kurama is unleashed and is once again fought over as a source of power. Spirit world begins to seal off the demons from human world but Kurama manages to stay by dispersing it's chakra. The fox cannot maintain this state forrever though and eventually in order to stay in human world Kurama asks Sakura to seal it inside the body of the last Uzumaki: Suichi Minamino Uzumaki. Sakura continues to live on, steadily collecting chakra and storing it behind her forehead. She uses her power to prolong her life. She develops her own techniques, and she wants to pass them on along with her massive store of chakra. She chooses Yuske to be her student. He reminds her a bit of Naruto. Eventually Sasuke thinks he has found the ultimate opponent in Yusuke as spirit detective and Sakura's student. He 'invites' him to participate in the dark tournament. Yusuke's team is all the same except that Genkai is Sakura and Kurama/Suichi is a Jinchuriki. Sasuke learned edo tensei from Orochimaru and builds his team of resurrected Naruto, Kakashi, and either Tsunade or a younger version of Sakura.