Obsession.
Viktor and his family were helping to defend the library. The attack was quite strong and the demons really put a lot of effort into damaging the place.
It seems they wanted to destroy the source of learning of the place.
'Or maybe it's for something else' Viktor thought, however he didn't know a specific reason besides the previous one.
The lower demons were not strong for the family, but they were strong for ordinary humans.
They were also characterized by their sheer numbers, aggressiveness and complete submission to their superior demons.
Their attack was not dangerous to the family but they could not avoid all the damage. The interior of the library was still in good condition, but the outside was damaged.
Braimhs was noticeably disappointed, frustrated and angry. Viktor tried to comfort her a bit, but didn't think it was a good idea to say much after seeing her and knowing her mood.