Mangekyou, me guessing.

[Shalev]

I feel, how to unlock the mangekyou sharingan, is by seeing your closest friend die in battle,so the people who possesses the sharingan; truly don't need to kill their own closest friends, because that's what happened to kakashi, it's like Gohan using the "pain of loss" __
it's like the sharingan has a trigger or an amount of images to be seen until the eyes "cry".
cause crying releases "sadness and sorrow".

 

[Q of the Sharingan]

That would explain why Sasuke was shown with tears in his eyes when he first showed his MS.

 

[panther27]

sounds right

 

[EternalSage]

Still don't know exactly how Kakashi obtained his MS, but Sasuke got his MS after killing Itachi. And Sasuke got his EMS after implanting Itachi's eyes.

If you're an Uchiha the process is laid out.

 

[panther27]

yea the process seems laid out but i wonder how madara unlocked his rinnegan

 

[Shalev]

kakashi's sharingan was implanted though, meaning it's a one way process?

 

[Universal Enlightenment]

its feeling a great amount of emotional pain.