Well..
The First idea i had was , when u are an anbu black op , and u wear the mask your identity is hidden and when u take it off your identity is back to normal.. so anbus are secret ^^.
Also When a person becomes a kage, each kage has 1 speaical jutsu.. that only kages can have.. but only if they are worthy and village votes for the kage.
XD thats all i have for now But ill be back!