Well, this may be a little late, so you probably already know the answer but it was Granny Chiyo. She uses a forbidden jutsu, that she an others had created but with deadly consequences.

He didn't reincarnate, he was brought back to life by Granny Chiyo.
Wooh, best character died AND came back to life! 🙌
(Gosh, I'm late at answering this, everyone probably already knows this...)