So he can't channel chakra through his hands because his arms are *literally* missing their "soul"? Like, he has soulless lumps of flesh just hanging off of his still ensouled shoulders? So the soul isn't just like, a mass of spiritual energy and/or consciousness that possesses the physical body... but an actual detailed spiritual analog that anatomically matches to the physical body it overlaps? Like, there is a spiritual equivalent to all of your physical organs? Do you have a "soul liver" in addition to your actual physical liver?
What a bizarre idea. How does spiritual amputation work with other organs besides the arms? What if someone amputated your spirit-lungs? Would you just lose the ability to channel chakra through your breath (so no more fire jutsu) but be otherwise fine (assuming a medic treated you)? Would amputating someone's spirit-stomach prevent them from swallowing impossibly large objects - like Orochimaru and his sword, or Naruto and that giant scroll-toad and Itachi's raven? Could you disable an Uchiha's sharingan by ripping out their "soul eyes"?
What about people who have lost their physical arms - do they still have invisible soul arms where their physical arms used to be?
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I wonder if there is a limit to what jutsu can be used without handseals. The subject is almost never touched upon in the manga or any databooks to my knowledge. Hmm.
Sasuke learned how to use the chidori and a number of variations of it without needing handseals over the timeskip. Is it possible to learn how to drop the handseals from any elemental jutsu, or do you need to have a strong affinity for that element for such a feat to be possible? Could Sasuke potentially also learn how to use his fire jutsu without handseals but never felt it was worth spending the extra effort and time needed to do so?
Jiraiya told Naruto once that the Rasengan
"has a difficult seal" but he didn't want Naruto to learn it that way ("just using chakra is good.") I assume this means that it is possible to perform the rasengan by using handseals instead of mastering the three stages of chakra control (rotation, power, containment) but that wouldn't have improved Naruto's abysmal chakra control so Jiraiya refused to teach him that method.
If Rasengan, an A-rank jutsu and the highest level of shape manipulation, has handseals but can be learned without needing them... does that mean that any other jutsu can potentially be learned the same way? Are handseals just a crutch that are commonly used because most ninja don't have to skill and/or time needed to truly master more than one or two jutsu?