Echoes of the Forgotten Sentinels

Imagine a world where heroes like Power Rangers existed long ago, but were forced to go into hiding after a specific incident, kinda like The Incredibles. The world has been somewhat calm in the hundreds of years since the incident, and the heroes are now nothing more than legend. Now, centuries later, the powers of old call upon a new generation of heroes as the old threat, the cause of the incident, rears it's head once more to claim a world once thought to be theirs.