Ninhito, welcome to the Board.
I think you will find, as you read thru some of the posts, that a lot of the Fantasy aspects of Ninjutsu/jitsu are just that, fantasy. Take some time to read the previous posts, and let them help formulate an idea of what real ninjutsu/jitsu is.
I personally have never seen shuriken with rings on them, but that is not to say they dont exist...
In the Bujinkan (the organization I belong to) it is my understanding that Kuji is only taught to higher ranking students... perhaps one of them could elaborate if you ask about it in the traditional section...
Again, welcome to the board!