Good call on unequipping weapons. I figured that just swapping in some archers from my defense team instead of Tiger of Kai, Master Strategist, and Sanada Yukitaka would be enough, but no, they instantly die of reflect damage, too. So I had to also unequip their weapons. I accidentally unequipped a weapon from the wrong general, leaving poor Mori Motonari to die of reflect damage in the first round.
Good thing that the battles with the good loot are the 5th and 6th ones, so we can just ignore the 8th battle. I've already got 33 of vol 1 and 17 of vol 3, so vol 2 is the one that matters.