The storytelling of the manga overall is a little clunsy here and there, but man if this chapter wasn't PEAK!
The deux ex katana is a little lame, but i belive it's more so our girl has an fighting chance agains the dude magic armor, and i think it's an payoff to her saying she has low mana and learned to fight with no mana all the way back in chapter 2 or something? Was it ever been said that people with high mana die faster when the mana gets low? I dont remember.
Oh well, still some great scenes this chapter!
Thanks for the translations!