Possibly the Greatest Alchemist of All Time S01 E11

S01E11 Signs of Turmoil

Máni joins the Wings of Nolyn as they build the fortress town of Wedgefort, which grows more prosperous by the day. However, the Holy Empire of Sidonia activates their Hero Summoning, which causes the mana in the region to fluctuate, increasing the strength of the monsters outside the fortress' ramparts.