During the prologue mission (00), you will be facing Metal Gear Ray. This trophy is attainable during the first encounter with Ray.
In order to get this trophy, you need Ray to swing his tail. I found staying about mid distance from him will initiate his tail to swing. Just block the tail (imminent incoming attack direction + X) and Blade Mode will be initiated. Just keep slicing up the tail as much as you want, and the trophy will pop after you hit the ground.
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