The sword used in the current fight is a different magic sword than the one they discussed in the beginning. The sword that broke was a regular magic sword I believe while the current one is their holy sword. The current battle going on is what they have been preparing for during the last several chapters. It was never given a large amount of panels when referenced though. But you can find different panels addressing the big spider and how much of a problem it was.
The negotiations were supposed to aid the demon kingdom in their fight against monsters in exchange for silver. But then that blew up due to the duke’s plotting. So along the lines of:
Thor sent as sacrifice -> thor becomes asset to demon king -> duke butler realizes the royal magic sword can’t be repaired due to Thor being on and request for the appearance to be fixed -> princess outs duke saying she barely survived the final monster attack due to whoever did the actual magic sword repairs -> duke’s prestige falls due to poor repair of royal magic sword -> duke attempts to recover by having demon duke betray his kingdom -> demon duke said hell nah and reported it -> empire said the plot had nothing to do with them and shows no interest in caring about Thor -> demon kingdom becomes even more distrustful but not resentful of people from the empire -> thor makes laser beam to help with upcoming subjugation of spider monsters -> demon king army discusses plan for JOINT subjugation with empire -> while preparing the empire attacks monsters alone in an attempt to take all of the glory -> demon army had to come save their dumbasses
Eh. Am I the only one confused right now? Like is chapter 13 a flashback to when she broke the sword or is it a different fight? Like one chapter they were talking about negotiations and next bam. They fighting.