It doesn’t seem to be the case that the user of Reversal always uses their power-increasing item before Reversal takes effect. While battling the AI, on multiple occasions, my opponent’s Reversal has taken effect first, followed by my sword item, followed by their power item. (Recently I’ve noticed this once when the enemy has used a sword, and once when it has used a stone.) I do, however, recall at least one instance in which I’ve used my sword item before Reversal. (I think it was my own Reversal, so I effectively powered up the opponent’s monster when I thought I would gain a large advantage.) It surprised me at the time, and as Robin001 seems to imply, it doesn’t seem particularly fair unless there’s some clear and consistent method to the ordering of these effects.