This is one of my favorite set of pages thus far because it's so vague but with so much potential. I don't think it's fuuton Rasenshuriken since I don't think he knows about Naruto pursuing this, it was Kakashi's idea.
First, the toad key says that he's not ready yet, which could refer to the need of sage mode for the jutsu.
"That" jutsu I think refers to the jutsu only Naruto as the Kyuubi Jinchuurrikii can perform. Before the fight with Pein, the toad may have felt Naruto didn't need it, perhaps because he had Jiraiya. I think that with Jiraiya killed by Pein, which he didn't expect, the need may now be there.
I think FTG is a technique for Naruto, a kekkei genkei, or something only the fourth should have. Minato believed in handing down his best jutsu, and the only one not handed down is FTG, which I describe in an earlier post. Basically I think the jutsu requires a strain on the body or is blood limit; thus only Naruto will know.
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