How is Kakashi able to get Mangekyou Sharingan? I read what happened with Rin. 

If Kakashi is a copy ninja, how is he able to get the Mangekyou Sharingan without the Uchiha bloodline?
Short answer.

Sharingan wielders don't really have to be part of the Uchiha clan to activate the Mangekyou Sharingan.


  It is initially awakened by the trauma suffered from witnessing the death of someone close to the user.


So you just have to have a Sharingan and witness the death of someone close to you.

Sources:


Mangekyou Sharingan