HPXNaruto
I know that HP isn't for everyone but HEAR ME OUT!
Someone from Naruto dies and is reborn into Harry Potter but as Regulus Black. That probably sounds a bit familiar and for what it's worth, I love those stories which is part of why this all came to mind. Usually the person being reborn in this case is Uchiha Itachi. But-
BUT-
I raise you either Uchiha Izuna or Senju Tobirama.
If you have an opinion on which would be better over the other, or want a longer snippet let me know. But here are my thoughts with both.
Uchiha Izuna: Either gets reincarnated immediately post ocular transplant/dies or his ghost kind of sticks around and sees Konoha be built and how that all ends. The best part of this, in my opinion, is he would get a brother again, Sirius, who is both similar yet different to Madara in all the right and wrong ways simultaneously. The problem arises when even his new brother chooses sunshine boy (Hashirama/James) over himself slash their family. Just picture the angst. Whatever magical gifts that the Black are known for, this boy is going to have them all if only because he has never, not once, put anything over FAMILY.
Senju Tobirama: Tobi would get reincarnated post fight with the Kinkaku/Ginkaku brothers. He wakes up in a family, in a body, that is surprisingly not all that different from what he was used to. He knows exactly how to deal with James because that was Hashirama, right? With this one, the exploration of genius/scientist facing everything that is Voldemort/Tom Riddle? I seriously think that Voldemort would come to really appreciate the Black family more than he already did via old classmates/Bellatrix. You would probably see more political happenings because this Regulus/Tobi would not stand for the whole mudbloods are lesser. He would clock this Dark Lords racist ideations as the fear that it is and, what, become Voldemort's PR specialist?
Thoughts?
(It should be noted that I actually already have an HP sorting post related to this, but Izuna would either go Slytherin/Hufflepuff (Probably Hufflepuff in this for drama sake) while Tobi would obviously go into Ravenclaw. The Blacks could disparage Sirius for his sorting but their golden child? Hell nah.)