Hello,
This interface was replaced with the Exchange interface, found in the upper right hand corner of the Recruit interface. The link is dead but this new system/interface exists and can be used to complete the missions there.
Hopefully the link gets fixed soon and the text updated, sorry for the inconvenience!

It can be completed. I believe you simply have not done so yet. I believe it is asking for the total number of stars of your ninja. If you star up a ninja or get a new ninja that number should increase.

Any and all ninjas should count. Try starring up any ninja. You should see your number in this interface increase.