LERAYE'S POV:-
Waves or more precisely waves of monsters occurs when there is an extremely high disturbance in the mana at a certain place. The higher the mana disturbance the more better the quality and the quantity of monsters it will attract. Waves can be good or bad depending on how, when or where they occur. Obviously for Eslaine it's more of a boon than a bad thing. It is also a good thing for young adventurers to increase their skill and experience. Plus it also helps in testing the defenses of the city of Eslaine against monsters and other threats.
Generally the waves are known prehand within the city by the people and they prepare for the waves accordingly but because of Leader's brainwashing everyone forgot about the mana surge that occurred during the attack. Even still the higher ups alerted most of the adventurers and soldiers to prepare for this scenario so the city should be safe.
