Note: This solution can also be used to earn the S Rank achievement for a 2-for-1 deal.
For this trophy you'll have to earned an A Rank for the Overcoming Hatred Boss Battle between Naruto and the Nine-Tailed Fox.
For FACTORS on reaching high Rank for Boss/Pseudo battles please consult with this trophy solution:
This is one Boss Battle, divided into 2-parts due to a lengthy cutscene, so you'll only be getting 1 Rank.
The first half of the battle you can choose to fight the Fox yourself, or with the help of Killer Bee, based on the Legend or Hero decision. And from there your battle will commence until the cutscene.
The second half of the battle will be Naruto with the help of his mother, Kushina Uzumaki.
After you've prevailed over the Fox, Naruto will reach a new level of power, Kyuubi Mode!
If, for any reason, you aren't able to earn an A Rank no worry. You can retry ANY battles post-story in the Ninja World timeline for another try.