For this trophy you'll have to earned an S Rank for the battle of the Hero and Avenger with Naruto vs Sasuke.
For FACTORS on reaching high Rank for Boss/Pseudo battles please consult with this trophy solution:
This battle will only consist of one part as you face off against your lost-lost friend, Sasuke Uchiha. This driving battle will even intertwine with flashback battles further drive you to win. With cinematic flare, and IA's you'll work battle with all your heart in search of an answer.
Once you've finished the battle with an S Rank you'll also earn the "A" rank trophy!
If, for any reason, you aren't able to earn an S Rank no worry. You can retry ANY battles post-story in the Ninja World timeline for another try.