Originally posted by: WarkWark
As far as I know, and I just watch the anime, but have been bored lately due to uber-filler, Kakashi is the only person still alive, who has seen Mangekyou while having his sharingan activated, Itachi also used it on Sasuke, but I don't remember sasuke having his sharingan activated at that time, so possibly kakashi has made an original technique based on what he learned from his run in with Itachi's Mangekyou. I know its a bloodline limit technique, but if you think about this, Rasengan the technique passed down from the fouth hokage is probaly how Kakashi learned how to do his Chidori, I always saw chidori is a make-shift rasengan.

He invented chidori on his own.

And ya, he prolly sharingan'ed the mangekyou sharingan before he got owned by it. And over the years he developed an advanced sharingan to counter it.