Kagerou Daze/Snakes

Black snakes with deep red eyes grow from Azami's head as her hair, which is a typical feature of a Medusa, but ten with abilities were her most significant. These snakes were created from Azami's strong feelings and are manifestations of her instinctive wishes. Each snake has a set of supernatural abilities that it grants to its owner to help fulfill a specific wish; acting towards this wish is the reason for each snake's existence. Most of her snakes are solely driven by their drive to fulfill wishes and have no sentience beyond that primal urge, with the exception of the Snake of Clearing Eyes, which is the snake that gave Azami the idea of creating the Kagerou Daze,    and Konoha. The snake created by Marry, the Snake of Retaining Eyes, is also fully sentient. The snakes have been shown to be able to talk to their future and current owners in the Kagerou Daze itself,  and sometimes in the real world too. Their size and appearance vary across scenes, sometimes looking like normal-sized snakes, others like giant snakes, assuming human shape, and even as disembodied voices.

Snakes can act as a surrogate replacement for a person's life. When Shion and Marry were murdered by humans, Azami ordered the Kagerou Daze to swallow them just before their last breaths, since in the Kagerou Daze time does not flow properly. Azami then gave Marry the Snake of Combining Eyes, also known as the "Queen Snake", so she would be able to return alive to the real world. However, this caused Azami to lose control of the Kagerou Daze, and it continued her order to swallow up people who die on the day Shion and Marry did, August 15. To follow the "Queen Snake" that is now in the real world, the snakes began to leave the Kagerou Daze through the bodies of humans who entered it with a strong wish that was compatible enough, and thus could be fulfilled, with their abilities.

It is implied that a snake can leave its owner's body, thus killing them, if its owner's wish can no longer be fulfilled by its abilities, be it because the wish has been completely fulfilled or by other circumstances, and if its owner has no other strong wishes that it can fulfill. Even when the owner's loss of interest in their wish does not get to that extreme, snakes do not like when their owners do not indulge in their wishes, as those are their sustenance, and will thus goad them into acting upon it, even if it brings suffering to their owner. In the case of sentient snakes, completely granting a wish with no other to fill the gap can make them "disappear".