This trophy is titled "This Just Got Real" and it requires that a double down occurs. Double Down is another term for draw, meaning both players K.O each other at the same time. Good luck if you plan on doing this one against the AI, it's tricky to get the timing down even with a second controller.
Theoretically this could be rigged up with any character using two controllers however I preferred using Ragna. Your first step will be lowering both controllers down to a sliver of life. Then, get a little bit of space between the characters but not so much that the attacks won't land. There are two moves I've found to be effective, that's tapping triangle or flicking the Right Stick to the right and doing Gauntlet Hades. It might seem simple enough to press 2 buttons at the same time but you'd be shocked how many times you can mess this up. It's worth noting that Gauntlet Hades is flicking right on both controllers, it doesn't change depending on which side you're on.