I’ve been following the My Hero Academia manga since the first anime came out, but it hasn’t been until recently that I’ve had a chance to catch up completely with the anime. It’s been a fun watch even if I already know the outcome. However, I did catch something that I missed when I read the manga the first time: specifically, it has to do with the aftermath of Iida, Midoriya, and Shoto’s battle with the Hero Killer Stain.
Those of you with a keen eye, and some knowledge of human anatomy, have probably already figured out where I am going to be going on this one. For the rest of you let’s start with the obvious question, what is the brachial plexus?
To begin with the brachial plexus is a real anatomical structure in the human body that is important to the function of the arm and hand. So, the manga, and by extension the anime, is correct in that regard. However, it is not just a nerve, it is a network of nerves that runs from the outside of the neck to the armpit.
The network is formed from nerves leaving the spinal cord; specifically, these nerves are from the cervical nerves 5 through 8, and thoracic nerve 1. These nerves control the arm and hand, plus carry the sensations detected on the arm and hand back to the brain. Lastly, this network is called the brachial plexus, not the brachial plexus nerve, because it is not a single nerve but a combination of multiple nerves.
I can, however, think of a few reasons as to why Iida uses the term brachial plexus nerve. The first is that the translator either translated the term wrong or added the word nerve to provide clarification to readers who do not have knowledge of anatomy. (I have to give props to the English Dub of the anime which simply calls it the brachial plexus.) The second is an in-universe event. Iida’s doctor calls it the brachial plexus Nerve to help explain his injury as Iida is only a Freshman and would not have advanced knowledge of anatomy. The last is that the writer of My Hero Academia, Kōhei Horikoshi, used the term brachial plexus Nerve to make Iida’s injury sound more severe. Now you might ask, why did you say he might have used it as clarification of the injury like a translator might have? Well, that leads into the second half of the article and what prompted me to write this in the first place.
Iida didn’t actually hurt his Brachial Plexus
Yes, you heard me right, based on the closeups provided by the manga and the anime, Iida did not injury his brachial plexus.
In both the manga and the anime, we can see that Iida’s injury is not in his shoulder, but on outside edge of his upper arm away from his armpit. When we look at the location of where the brachial plexus is located, we can see that the location of the injury is nowhere close to it.
Additionally, we can see from the diagram above that the major nerves of the arm run on the inside closer to the armpit rather than the outside of the arm. So there really aren’t any other options when looking at Iida’s upper arm injury.
So which nerve did he actually injure?
In this case I only have one other option based on the injuries Iida received at the hands of Stain and that is to see what nerves could have been damaged when Stain stabbed his lower arm (wrist).
Lower Arm Injury
The first and most obvious problem is that the lower arm injury is on his right wrist and not his left. The second is that there are several possible nerves that could have been damaged in the attack.
If I had to make an educated guess, I would go with the median nerve because it appears that the knife went through the middle of his wrist. In the anime it appears that the knife went through his wrist impaling it to the ground, which it makes it likely that the knife damaged the median nerve. Also, an injury to the median nerve would cause muscle and sensory problems for the hand.
One thing the anime and manga do get right is that Iida informs Midoriya and Todoroki that he will need surgery to heal his injury, specifically a nerve transplant. To the uninformed viewer this might seem like a fantastical science fictionesque plot device. However, nerve transplants, or nerve grafts as they are also called, have been around for a long time. It first appears in the historical record all the way back in 900AD where it is mentioned in the writing of the Persian doctor Rhazes. The first actual record attempt at a nerve transplant was in 1885. They became more common and successful after WWII. In most cases the surgery removes a nerve from the leg that serves the side of the foot or a nerve that serves the armpit. It does result in numbness in the area the nerve was taken from, but it does lessen over time. The other major issue is the length of the graft, with grafts of over 15mm recovering about 80% function. I have no way of knowing how large a graft Iida needs, so I can not determine the effectiveness of the treatment, but since he mentions the possibility of permanent damage, I would guess that it is a larger graft.
Based on the information given in the anime and the manga there is no possible way that Iida could have damaged his left brachial plexus. The stabbing injury he received from Stain in his left upper arm is just not even close to where the brachial plexus is located, let alone other nerves in the left upper arm.
It is much more likely that he damaged the nerves in his right lower arm (wrist), and that it should be his right wrist and hand that should be impaired.
In any case, regardless of where the nerve injury is or is not located, the treatment of a nerve transplant or graft is highly likely if any of Iida’s nerves were severed.