I was thinking, the Yata mirror has to have a weakness, perhaps it requires the person who uses it to put in as much chakra, as the used in the opposing jutsu. If I am correct, then the Yata mirror will be useless against very chakra taxing jutsus. And since Kirin is natural energy and was guided by the Chidori, I think that Itachi just put in chakra for the Chidori, because he lacks the reserves for Kirin itself. Your opinion?