I kind of wish they'd kept the Tranquility Girl the way it was in the LN. If I remember right...
Spoiler:
The group was actually out looking for monsters to kill, maybe even that particular monster, due to the fact that it's one of those special kinds that has essentially no strength, defense, or hit points, and immense amounts of XP, but people still aren't able to kill. Kazuma's level had fallen a bit behind, so he wanted to play catch up. When he went back to ask her not to "attack" other people coming by, he caught her pulling the same act with the exact same lines on another adventurer, and again managing to get out alive but after he left complaining about how she can't seem to catch any good prey. Her death is basically the same, but then when he comes back happy and proud to have leveled up by such a large margin so easily, the others ultimately catch on to what happened and break down in shock that he'd murder such an "innocent". He managed to clear up the misunderstanding, but it took some time.
Still, I'm delighted they finally brought her in, I really liked that bit.
And I guess this's Kris's payback for all the panties she's lost over the year or so since she met him.