The Secret Story of the Strongest Tag Team!! (最強タッグ秘話!!, Saikyō Taggu Hiwa!!) is chapter 542 of the Naruto manga.
A's flashback continues. The two "brothers" go on several missions together, on one of which they are joined by Killer B's cousin. A and B's cousin discuss the possibility of Killer B becoming the next jinchūriki of the Eight-Tails. A wonders if B will have enough control to suppress the Eight-Tails. B's cousin reflects on what it means to be a jinchūriki, and despite outwardly appearing to have everything, what a jinchūriki really needs is something to fill the hole in their heart and give them strength. Later, A and B are shown attending B's cousin's funeral. A sets B the goal of matching his own strength, to which B replies that someday he will surpass his brother. The day arrives when the Eight-Tails will be sealed in B, and A tells B that from here on out, things will be different. They bump fists, and A says that no matter what happens, he'll be there for him. Sometime later, A clashes with Minato for the first time. Minato commends B for his bravery, and tells A that he should find out his brother's values as a person — what B holds most important — before he became neither a human nor a jinchūriki.
In this chapter, when A and B face off against several Iwagakure shinobi while on a mission, B is first depicted with longer hair. However, in subsequent panels his hair is once again short and spiky.