So "That" Jutsu that Naruto will use is

[SageOfTheTenPaths]

Banbutsu Sōzō

Spoiler

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He and Sasuke will join hands and use Banbutsu Sōzō to create som kind of new jutsu to defeat Kaguya.

 

[Solog0d]

what if Genjutsu > kaguya?

 

[CloyEscapade]

They're going to do the fusion dance

 

[LordNarutoSo6P]

Yeah, I have the same thoughts with you buddy!