Every thirty years they come. Vile creatures who seek us destroyed or enslaved. We have gotten better at fighting them now our people know the pattern and what we must do to stop their onslaught.
The Precursor comes first, their champion and first wave. More than just a show of force it acts as an anchor to their realm everyone it kills strengthens the portal to come. The Slayer of the precursor becomes our champion, the weapon used to put down the beast becomes a symbol for our struggle and the only thing that can end the war.
Once the Precursor is slain we have less 6 months to prepare for total war. Our diviners seek the location for the portal and our champion prepares their army for the attack. If the gods favour us we can end it in one quick brutal battle. If not all nations must unite to end the threat for another generation.
When the battle is won our champion must attack the portal with the blade that slew the Precursor. This destroys the portal and consumes the power of the blade.
Once the portal is closed we begin the cycle again, train our children to become the next champion. Train our diviners to find the next Precursor.
The cycle never ends but we know the price for failure nations have been lost generations enslaved. Our allies have sent armies through the portal to attempt to stop them returning. All for nothing. The Precursor always comes.