This trophy is titled "I Am the Just Sword" and it's for defeating Hakumen in either Arcade or Score attack. Unlike most trophies for defeating characters, this one has no "Unlimited" requirement, so it's naturally much easier than those end up being. By naturally facing him in arcade mode or towards the end of score attack you'll end up facing him down the road. Watch out, his range and power are definitely his strong suits and he doesn't even lose that much speed in the process.