1. Kakashi is somehow forced to kill Rin
2. Obito witnesses the killing and forces the Fourth Mizukage to continue the Bloody Mist tradition as a means to obtain vengeance
3. The Senju/Uchiha combination somehow allows Obito to use the MS without lose of eye sight.
3. Killing Zetsu cripples Obito.
4. After this flash back Obito dies (lol we all know its coming)
I still don't understand how Madara gave his eyes to Nagato. Wouldn't Edo Tensai Nagato not have the Rinnigan? I'm not disputing anything I just think its a plot hole that demonstrates a lack of foresight.