Naruto's first futon rasengan's weren't able to be thrown but still had the spiral effect on them, which Boruto's is lacking. In case you've forgotten, which it seems you have this is what a rasengan looks like with fuuton added.
It wasn't until he used senjutsu with it he could stabilize it long enough to throw. Chapter 339 the first time he uses Rasenshuriken and his eyes are in Kyubi mode
If you keep reading to 340 you can see even though this is Rasenshuriken he doesn't throw it
Rasenshuriken is just the name of Naruto's Fuuton Rasengan not just the version that can be thrown.
Skip ahead to chapter 415 and we get Naruto learning Sage mode and getting the idea he can throw Rasenshuriken
The first time we see a hint of a thrown Rasenshuriken is chapter 418
So as you can clearly see, Raenshuriken is fuuton rasengan and was only able to be thrown by Naruto AFTER he learned sage mode. Yes I'm aware this sounds like I'm saying Boruto uses Sage mode but I don't think he does so consciously I think it's just something that happens. As for how he has sage mode, idk how the authors may choose to incorporate that and I am aware it's a catch to my idea but it would take the same amount of explaining as why suddenly adding fuuton to rasengan allows it to be thrown when it was shown not to work that way. Anyway just some food for thought.
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It wasn't until he used senjutsu with it he could stabilize it long enough to throw. Chapter 339 the first time he uses Rasenshuriken and his eyes are in Kyubi mode
You must be registered for see images
If you keep reading to 340 you can see even though this is Rasenshuriken he doesn't throw it
You must be registered for see images
You must be registered for see images
Rasenshuriken is just the name of Naruto's Fuuton Rasengan not just the version that can be thrown.
You must be registered for see images
You must be registered for see images
Skip ahead to chapter 415 and we get Naruto learning Sage mode and getting the idea he can throw Rasenshuriken
You must be registered for see images
You must be registered for see images
The first time we see a hint of a thrown Rasenshuriken is chapter 418
You must be registered for see images
So as you can clearly see, Raenshuriken is fuuton rasengan and was only able to be thrown by Naruto AFTER he learned sage mode. Yes I'm aware this sounds like I'm saying Boruto uses Sage mode but I don't think he does so consciously I think it's just something that happens. As for how he has sage mode, idk how the authors may choose to incorporate that and I am aware it's a catch to my idea but it would take the same amount of explaining as why suddenly adding fuuton to rasengan allows it to be thrown when it was shown not to work that way. Anyway just some food for thought.