Rc Cell Pathway Formation in Pure Ghouls
In chapter 37 of Tokyo Ghoul :re, Dr. Shiba reveals that half-ghouls like Kaneki and the Quinx can become stronger due to the formation of Rc cell tubes.
He explains that these Rc cell tubes are formed when their bodies are injured, and then goes on to elaborate how Kaneki’s Rc cell tubes are much more numerous than those of the Quinx due to the numerous injuries he’s endured in the past. This prompts Urie to begin strength training to tear his muscles so new Rc tubes will form to repair them.
However, it is never stated in the story if ordinary ghouls can become stronger in this manner as well. Do Rc cell tubes form when ghouls are injured? Or, since ghouls rely solely on Rc cells for nutrition, does that mean these pathways are fully formed in them from the start? In the story, I've found one such case of a ghoul being drastically injured and then gaining a power boost.
Ayato’s Sudden Power Boost
At the end of the Aogiri Arc in the original Tokyo Ghoul series, Kaneki broke half of Ayato Kirishima’s bones in the infamous “103″ bones scene.
Months later, after Ayato has recovered he begins killing ghoul investigators as the “Black Rabbit” in order to draw the CCG away from Touka’s trail. During the scene we are shown of this, Ayato only uses the left wing of his kagune (probably to mimic Touka whose left wing was much larger than her right at this point). However, the size of the wing itself was much larger than it was prior to the timeskip (and prior to the bone breaking). For comparison:
Dr. Shiba stated that rc cell tubes exogenously formed the kagune. So, by that logic, more tubes should mean a larger kagune. So, could Ayato having half his body broken have forced the formation of enough rc cell tubes to explain this huge kagune increase? While ghouls can heal more quickly than humans, Ayato’s rc type is Ukaku as opposed to Rinkaku (meaning he can’t rapidly regenerate). Therefore, having half his bones broken means that even Ayato would be down for a while. After recovering, Ayato would have had his Aogiri duties, and thus probably not a lot of spare time to train. So, the creation of new rc cellular tubes seems the most logical answer to his sudden power creep.
After hearing how half-ghouls can get stronger “the more they get hurt,” Urie decides to train to tear his muscle fibers to form new rc cellular tubes. However, Dr. Shiba never stated a particular way of getting hurt that would form these tubes the most effectively. Ayato’s method (broken bones) may be the most efficient method of doing this due to the nature of rc cells.
Rc Cells in the Blood
In a post titled “Ghoulology 101″ by @coromoor it goes over how rc cells are presented as a type of human blood cell. This is supported in-story as rc cells resemble “curled-up fetuses” similar to blood cells afflicted by sickle-cell anemia. Furthermore, rc cells have been shown to heal many different tissue types (skin, muscle, bone, etc.). To be able to do this rc cells must be able to differentiate into different cell types like human blood stem cells.
However, human blood cells are formed in the red marrow. Red marrow is primarily found in long and flat bones: hip bones, breast bones, the skull, the ribs, vertebrae and shoulder blades, and the proximal ends of the femur and humerus. So, by association could we assume that the majority of rc cells are formed in these bone as well? Also, if these bones were damaged, would rc cellular tubes form due to the interaction between rc cells and the red marrow? Finally, would the tubes to these bones more numerous than to other areas of the body?
The answer to all three of these questions seems to be yes based on another aspect of the “Ghoulology 101″ post.
As pointed out in Kaneki’s rc scan, the most concentrated areas of rc tube formation are around the bones where red marrow is primarily found.
Conclusions
Ayato horrific injuries and subsequent power boost seem to indicate that rc cellular tubes can form in pure ghouls the same way as they do in half ghouls. Additionally, the way in which he was injured shows the quickest and most efficient way to form these pathways. Bones are simple enough to break symmetrically (something Kaneki mentions when torturing Ayato), and breaking them means the rc cells that move to heal them come into contact with the red marrow inside of them (the source of rc cell formation).
While red marrow is primarily found in long and flat bones, trace amounts are found in the other bones as well. So, the quickest way to fully develop the body’s rc cellular tube network would be break all of the bones in the body. Doing this all at once would kill someone, but doing it gradually over time would counteract this. While this of course would be painful, ghouls have accelerated healing so any damages could be reversed soon enough.