Like regular supernatural creatures, kitsune are featured as being bound by certain metaphysical rules. Being the tricksters, however, the rules that govern kitsune are rather subtle. These restrictions affect their everyday life as well as their nature and talents.
Fox spirits & Canine werecreatures
It has been featured in stories and stated several times that foxes and wolves do not get along. This wild relationship is reflected in the kitsune's supernatural repercussions regarding that of a canine werecreature. A kitsune's abilities seemingly have an adverse effect when exposed to a canine shapeshifter.
Stiles Stilinski: You can't be a Fox and a Wolf.
If an alpha were to bite a kitsune, they'd lose their kitsune abilities by changing into a new canine shifter, like a regular human. The bite can also exorcise a nogitsune of its host because the body is changed.
Foxes, in the real world, are solitary animals. They are known to be notoriously pesky and rely on their cunning to survive. In contrast, wolves, coyotes or other pack animals are innately predators, but also social creatures. Wolves are more direct, forthcoming and follow a code of loyalty.
One particular kitsune, a nogitsune who had renounced his humanity, went on a terror spree while operating by his own rules as he saw fit. More than just simply his monstrous nature, he appeared to play by these rules as if they were to come by naturally.
When this Dark kitsune was first summoned by Noshiko Yukimura, Noshiko had intended for him to possess her to escape death and seek justice for a mass slaughter. However, it's stated that kitsune are not meant to be used or controlled, commanded by a master. This could be because of the rule that foxes are solitary creatures, they are more freedom minded.
In mythology, kitsunes are commonly portrayed as tricksters. They are known to play games, tricks with their victims. In order for a game to be played, it must have rules for the players to operate by. Languages, for instance, don't follow a fully concrete set of rules as they are often complex, interchangeable.
In Season 5, Kira found she is unable to read the coded novel featuring the para-scientists, the Dread Doctors. The novel had been written by Gabriel Valack to work as a tool to trigger the memory senses of the brain to uncover a victim's repressed memories.
Mason Hewitt offers Kira input with a theory that fox spirits have difficulty with language. He recounts a myth where people could identify kitsune. When answering a phone call, the receiver would say "Moshi, Moshi" ("hello", in Japanese). They'd say the word for hello twice which would promptly confuse a kitsune because it's a language trick. He surmises Kira can't properly read the novel because the entire coded story is one big language trick and it's confusing the Kira's fox part. Noshiko confirms this theory and instructs Kira how to overcome this issue. The story was the confusing factor for the fox, so she should read the book but not follow the story; she should read it backwards.