As Burkhart-san says, this dragon golem’s outer shell is entirely covered in mithril. Our magic doesn’t breach it at all.
Furthermore, because it is continuously spitting out a strong breath attack, we are currently huddling together in a state of being protected by Burkhart-san’s magic barrier.
“We can defend against the breath attack and such things as its physical attacks with its tail using the magic barriers of Wend and Burkhart-sama. But what will we do from there on?” (Luise)