Hello, by complete the last page you mean unlock all achievements or unlock some illustrations in the gallery ?
Viewing post in Naruto: Kunoichi Tactics comments
If you accumulate 200 war effort point you unlock a boss fight on the mission map, the boss respawn every few day so that you can do it with different kunoichi/outcomes. Those are the last illustrations of the gallery.
For the secret achievements take a stroll at night and search for a place where you can spend some time on your own.