The nudity in this manga really just comes out of nowhere, there's no reason for it and it's not because there's a lot as a selling point or anything, just sometimes the author just goes, boob time, and we get some boobs.
I'm going to guess Karen (the annoying tsun fire mage with the most unfortunate, yet probably accurate name given to her in these modern times) was stubborn to try to beat the record despite the warnings because she didn't want to get bested by a swordsman or some dumb prideful thing.