• consequences of the Breathing Styles, from a medical student's perspective • part 2
- Sun Breathing - the most dangerous and powerful of all of them. It was first mastered by Yoriichi who had the mark, reason for which his body could withstand the style. Sun Breathing messes with the cellular cycle that all humans have, being the direct opposite of the demon cellular cycle (which has been genetically modified to reproduce continuously - immortality). The death of a cell is induced through apoptosis , which is determined by one of its chromosome's branch length. When that length is close to 0, the cell triggers its own programmed death - apoptosis. Sun Breathing, being too taxing on the body, speeds up that process - the damage to the cells spikes up and the tissues have a high aging rate - which is why you need a demon slayer mark to master it. And which is why the slayers who bore the mark died around the age of 25. Aside from that, Sun Breathing taps into the life energy of the body itself - the reason it was so hard for Tanjiro to use it more than a few strikes in a row is because Sun Breathing gathers the strength from the oxygen-reducing reactions that allow each cell to function properly. Burning that oxygen normally happens in a controlled chain reaction that ballances the import of oxygen and the way it s consumed, the CO2 resulted being also eliminated from the body through a controlled process - through the blood, into the lungs, then out in the air through breathing. Sun Breathing requires way more than that, so it messed with the cellular chain reaction of burning oxygen , destroying the balance - it burns way more oxygen that the cell has to offer - which ends up two ways : if the User forcefully continues to do it , the cells die (or regenerate if the user has a demon slayer mark) or the user has to stop using the Tehnique. And naturally, if the oxygen is burned at a higher rate and in a higher amount, the quantity of CO2 released is also higher, and it cannot all be eliminated through breathing anymore - the User is intoxicated with the CO2 in their blood. This is the reason Tanjiro lost his breath and became lightheaded / in an altered mental state (not able to hear, blurry sight, etc) after forcing himself to use the Sun Breathing tehnique more than he could handle.
This is why, to master Sun Breathing, they needed the demon slayer mark. It killed them around the age of 25 nevertheless, but it allowed them to use the tehnique until then, and not die even younger. As a consequence of this, the demon slayers who bore the mark and used Sun Breathing (aside from Yoruichi) were destined to die at 25 with no other exceptions. The demon slayers who bore the mark but DID NOT use Sun Breathing did not die exactly at 25 (but probably later), because the other tehniques were not as harmful. Additionally, the more they used the mark, the earlier they died. This is why Sanemi and Giyuu probably did not die at 25, since they did not use Sun Breathing and only required the mark for a few hours until sunrise.
Aside from these, Sun Breathing users have a naturally high nody temperature, and they fight in a constant state of a high fever. Their heartbeat is raised, over 120 bpm (the normal is 60-100 bpm) because their body tries to compensate the oxygen consumption and cellular damage the only way it knows how - raising the vascularization of each territory by raising the heart's frequency and the blood pressure (the high blood pressure is the reason the capillaries in Tanjiro's eyes snapped when he fought Daki).
Part 3
this is the med school talking out of me
