Mmmmhh, the swarm aggressor didn't attack the city in the WN and therefore wasn't killed, in the following chapters it was noticed a bit but just as another monster in this isekai, they decided to make it die in the manga but I don't understand if when it died it had a after effect or that crack thing was the vampire bombardment.
Note: the vampire attack is the closest they get to kill MC in the novel until where I 've read it, she just send suicide clones at mach speed crashing the city randomly, she is very smart and thought MC needed to feel killing intent or know the enemy to IK it.