This is what happens after Yugito and Roushi's death.
Carmaru: Why couldn't I save them? Why does Sharingan have a Mangekyo version, not Rin'negan. I need to improve my dojutsu and kill them all!
(Sage of the Six Paths appears)
Sage of the Six Paths: There is a Mangekyo Rinnegan. And you have just got it.
Carmaru: I do?
Sage of the Six Paths: You will learn that you can now use three Mangekyo Sharingan and copy jutsu after only seeing it once. Now, as a reward, may I whisk you away to a place where I will teach you all the jutsu that any Hyuga should know. Don't worry, we'll be back the second we left if you want to go back.
(For thirty days, Carmaru trains with as many clones as he can make learning as well.)
Carmaru: I see. So that's all there is to the Mangeko Rin'negan. May I return to the real world?
Sage of the Six Paths: You may. I now have nothing more to teach you.