Himari Noihara is a white cat demon who protects Yuto in any danger.
Himari Noihara is a white cat demon that comes from a line of spirit cats that
have served the Amakawa family for many generations, and it’s now for
her duty to protect Yuto
from any danger, which she refers to him as "Young Master". She doesn't
have any parents since her mom died after birth and her father was a
different species or wild cat. Her knowledge of the modern world is very
limited and she mostly speaks in an archaic and overly polite way. In
the past (when she was a white cat), Himari used to play with Yuto when
he was young, and the two formed a close bond with each other prior to
him leaving with his parents. She forms a closer bond with Yuto after he
remembers his past with her.
As a cat spirit, Himari has the ability to transformer herself from a cat to a human. Her full demon from consists of her having white hair, red eyes and claws, and black markings all over her skin. When Yuto asked Himari in the manga that why her hair is black even though she’s a white cat, she secretly reveals that she modeled it after Kuesu’s hair color, but she also said that she would rather have her mouth ripped off than admit it. Because she’s a cat, she also shares some of their natural instincts as well, such as being afraid of water (except when it comes to a bath or shower) and having a penchant for seafood.
Himari also exhibits to superhuman abilities such as speed, strength, and endurance. In her catgirl form, she gains a high level of agility as well as a boost in her superhuman abilities. When armed with Yasutsuna, she becomes a highly skilled swordsman.
If Himari loses her sanity during a battle, she turns into a berserker cat with an uncontrollable bloodlust, which Shizuku states is her kind's true nature-a demon who derives pleasure from the hunt and loses herself in the slaughter-and that the more she fights, the darker her heart becomes to the point that it's completely swallowed up by her own bloodshed.