Throughout the course of Demon Slayer, protagonist Tanjiro Kamado has faced all sorts of powerful foes -- including members of the Twelve Kizuki -- as part of the battle between humans and demons. At the forefront of this conflict is the Demon Corps, an organization run by Kagaya Ubuyashiki with the goal of protecting humanity from the dangers of demons.
As the leader of the Corps, Ubuyashiki, known by his subordinates as "Oyakata-sama," makes and enforces the rules demon slayers must abide by -- but one of these is noticeably questionable. The rule forbidding members of the organization from fighting with one another doesn't really make sense, and is possibly being used to feign compassion for the fighters working hard to make the world safe.
Why Does Ubuyashiki's Rule Against Fighting Stick Out?
The "no fighting each other" rule appears very arbitrary when the Demon Corps members' roles and requirements are put into context. In particular, the entrance exam that must be passed before becoming a member is so violent in its nature that any rules against fighting are invalidated. As the organization's leader, Ubuyashiki allows the Final Selection: an organized death match where hundreds of children are confined in a forest and brutally murdered and eaten by demons if they're not strong enough to defeat the enemy. After this, the very leader who authorizes this event reprimands members of the Demon Corps who fight among each other, as if the requirements for entry weren't based on the same violence.
This feels like a control move from Ubuyashiki, as the level of violence within his organization changes when and how he wants it to, in a way that likely only benefits him. It also comes across as a feeble attempt to show his subordinates he cares, when all evidence suggests otherwise.
Demon Slayer's Hashira are worked to death. There's no structure in place to ensure the members who pass the Final Selection get in-depth training on how to survive in their role, and these same children are consistently sent on life-threatening missions without so much as an adult to ensure their safety. It's clear the members of the Demon Corps are replaceable and dispensable to Ubuyashiki, so why is there a rule in place that bans them from fighting one another?
Fights Between the Demon Slayers Could Be Beneficial
Such a large corporation can't expect every person involved to get along. In many cases, fighting among themselves could alleviate a lot of the drama within the Demon Corps and make everyday cooperation far easier. For example, it's well-known that the Water Hashira, Giyu Tomioka, is disliked by the others due to his aloof, loner personality. This rubs his comrades the wrong way, making them think Giyu believes he's better than the others of their rank. Really, Tomioka just has poor social skills and an inferiority complex, so what is interpreted as arrogance is actually low self-esteem. When he says he’s different from the other Hashira, it’s because he sees himself as unworthy of the Hashira title and standing with them as equals.
However, because there's an explicit rule against the members of the corps feuding with each other, this misinterpretation is never clarified and Giyu remains disliked. This puts a strain on his relationship with the people he is supposed to work alongside and learn from, and makes unnecessary drama within the Demon Corps. Because of the tension, comrades have little to no respect for each other and are quick to throw others under the bus.
Again, Giyu was a victim of this when Iguro Obanai, the Serpent Hashira, wanted him punished and in shackles after the Water Hashira broke the no-fighting rule by clashing with Insect Hashira Shinobu Kocho to buy Tanjiro time. There is no camaraderie or fellowship within the Demon Slayer Corps due to drama that could be easily subsided with the allowance of fighting.
It could be argued that Ubuyashiki doesn't want the members of the Demon Corps getting carried away in arguments and hurting each other, but again, his final selection is based on trapping children in a forest with overpowered demons, so it's unlikely that harm to his subordinates is the leader's biggest issue. Fighting within the Corps could solve a lot of the organization's problems, making its members more cooperative and improving their overall proficiency and safety as demon slayers.