http://forums.narutofan.com/showthread.php?t=106576
it says 3 different Ms users and the Kyuubi's Chakra will unseal the tengu. Itachi and Kakashi have MS and Sasuke might have one.
Itachi=Tsukiyomi
Kakashi=Amaterasu
Sasuke will probaly have Susanoo
Naruto=Kyuubi when mad or when he messed up.
each MS can only be acheived by its own way.
Tsukiyomi=killing best friend
that is why Kakashi got his without doing that.
If sasuke does use his with kakashi and itachi at the same time while naruto is there in kyuubi for this story could take a sharp turn