S ranks are primarily driven by how much health you have remaining and the number of stars you have from the quick time events at the end of the fight. Oddly enough, the more stars you get the more health you recover. That said, you'll naturally want all of the stars you can get. Quick time events occur when the character icon begins to flash, so be ready once you see this.
This trophy is for the battle in which you control Naruto and he faces off against Orochimaru. It starts out as a standard fight would, so don't deviate from your usual playstyle. Simply bash Orochimaru until his icon glows after roughly 2 life bars. The inputs for the QTE are as follows...
After Naruto transforms in to the four tailed fox, the battle takes it's own shape as many of the others have done before it. This one is similar to the Deidara fight in the sense that you must fire projectiles at the boss. This time around however, you have snakes that he sends after you to watch out for. Simply attack them as if they were enemies and they won't reach you. I'd say stress this more than defeating him quickly, as health plays a part in the ranking system. Use O and then your attack so that you can fire rapidly and do a bit more damage whenever your blue meter fills. Time for more events:
Left Square O
Triangle Triangle O
Right Square O
Up Triangle Triangle O
With that, you'll have the secret factor and hopefully the S rank netting you this trophy!