flying thunder god technique was just seals on kunai that he invented, the only reason only he has it is because he was smart enough to make the seals, no one else has realised.
And he didnt exactly show off them kunais, its like someone inventing something and not telling anyone how they invented it, itd take ages for someone to make the same invention from scratch.
Doujutsus are being put into play way too much, getting a bit annoying.
Personally its something new, and yeah, high chakra might have something to do with it, but that means hes related to kisame
Then again an akatsuki is meant to ally with naruto (though i thought that was itachi?)
so maybe kisame and naruto become blood brothers...bloodline brothers...haha...whatever haha