CoR - My own way.

Vesarus is at the Citadel when this happens... he is actually looking for a cause of the bug-types being controlled by making his way inside the citadel... so it's kinda both for the Mission and the event

Soooooo this month stuff's going down with Nirmala, the goddess of beauty showing up and creating a large citadel of silk... also she wants to reshape the world and rule it and whatnot... Vesarus is obviously irked by a deity trying to reign supreme and figured that she just needed to be shown the potential of mortals, similar like what had happened in an event that occurred in his world before Vesarus was displaced to this world.

Vesarus heard the plea of Arlett to find the cause of the Bug-types falling under a certain spell and stop it if possible; even though he doesn't still fully trust Arlett, it did seem like a wise plan... Vesarus could've also listened to the suggestion to avoid fighting, but with both the moves Aeroblast and Fiery Dance at his disposal, he felt little reason not to investigate the citadel... where else could this source be? After repeated attempts to burn his way into the citadel through it's walls, but finding it ineffective, he engaged in combat with one of the weaker gatekeepers; taking it out, yet also alerting other bug-types nearby... he'd just have to be fast with his search then.
If he would find the source, he would definitely investigate it thoroughly for personal gain before attempting to stop it or if that would be impossible, retreat and gather samples for a possible cure... without her lackeys this deity would probably crumble, he feels; whether it is true or not is another thing entirely .

Vesarus is mine
Noivern and Lucario (the burning bug-type in the back) are belong to Nintendo/GameFreak