if you live forever, you will begin to dream

THE CHARACTER

the wiki is a mess, soooo quick summary:

- In a world of ninja living in the shadows of modern society, there is an omnipotent technique known as Shinrabanshou (literally "all things in nature" or "all creation") that inhabits a single body at a time, passing between hosts endlessly. It's difficult to master, and more often than not, attempts to use it will result in the death of the host; but it's highly sought after, since it can grant any wish in existence.
- During the later part of the Edo period, a doctor serving as the Shinrabanshou's host tries to use its power to advance medical science. He performs experiments on animals, but in the end, the doctor dies, and only two of his experiments succeed: a cat and an owl, cursed with both immortality and human sentience.
- They wander the world as animals for nearly a hundred years, and meet Koutarou Fuuma, a young ninja boy who teaches them to take on human forms in exchange for being allowed to experiment on them.
- Certain that the Shinrabanshou is the key to their deaths, the two decide to integrate with the ninja world in order to seek it out, and they spend another hundred years searching.
- Towards the end of that period, they meet a man named Akatsuki, whose clan is able to communicate with animals, and who recognises them as unnatural. He takes them in and names the cat Shiratama, while the owl soon makes himself a human identity by the name of Kouichi Aizawa.
- What happens next is a memory that has been erased from their minds: Akatsuki's wife, Asahi, is the host of the Shinrabanshou. After their son Miharu is killed in an attack on her, Asahi uses the Shinrabanshou to resurrect him, and it takes the opportunity to jump hosts from her to Miharu. Asahi's last wish on its power is for everyone to forget.
- Ten years later, Miharu is revealed to the ninja world as the Shinrabanshou's host, and conflict arises once again. Shiratama adopts a human identity of her own, Shijima Kurookano, so that she can observe the situation and steer it towards the result she wants: for Miharu to master the Shinrabanshou, and grant her the death she's been seeking.

Shijima's nature, first and foremost, is that of a cat. Unlike Kouichi, who makes an effort to integrate with society and act like a normal human, Shijima has never pretended to be anything other than what she is. She'll walk in a human's body, and she won't tell others what she is because she doesn't care to, but nor does she care to put on a façade just for the sake of avoiding suspicion. She defines herself as "a monster neither cat nor human"; she will be both and neither by turns, but despite what she says, her true nature will always be the cat.

And since that's the case, it's not a surprise that her personality is about what you would expect from a two hundred year-old cat. More than anything else, Shijima will strike a person as aloof. She's lived a long life and seen just about all she cares to see; while it's not impossible to get a reaction out of her, for the most part, there is an overwhelming air of detachment about her. In fact, she considers herself a "bystander." She has no desire to get involved with humans and their history, and instead, she acts as a spectator, observing but never engaging with the world around her.

It's not as enlightened as it sounds, though — she is just kind of a jerk, too. She's not always honest regarding herself, but when it comes to anything else, she is blunt like a full-force sledgehammer, never shy to say things that people don't want to hear because she doesn't care enough to keep her mouth shut. She has absolutely no finesse for social situations and it doesn't bother her in the least. She's self-centred, aware of others but lacking empathy for them and thus always able to prioritise her own goals over anyone else's; she's also lazy, preferring to take a direct route than manipulate her way through a situation the way Kouichi would. When talking about the heavy sacrifices that the students at Alya Academy made for their goals, Shijima simply claims that she sacrificed "time and effort" despite having done very little overall.

Cursed with a human heart and an immortal body because of a single man's hubris, Shijima is a bitter creature. She resents humans for their flaws, the wars they wage and the schemes they concoct for the sake of power; towards the end of the series, she reflects that when "[she] got a human heart, it was all despair to [her.]" She can be purely indifferent, but she can also be cold and cruel. There is a point at which her callous disregard becomes deliberately malicious, and it isn't always easy to know which is which. Sometimes, she'll speak harshly to people because she doesn't care about kindness, but there are often times when she crosses over into outright schadenfreude, finding either fascination or outright glee in the misery of others.

Still, for all her unpleasantness, her nature as a cat does lend itself to a few positives as well. She is, of course, curious. The one thing that has kept her entertained for two hundred years is a curiosity for the world around her. Even though she resents humans so deeply, she also takes great interest in how they interact with each other and the world, and she ends up viewing the world through the lens of a combined misanthropist-and-anthropologist. They're simple children to her, and yet, they behave in complex and unexpected ways; if there's one thing Shijima prizes in the monotony of her long life, it's the unexpected. Speaking to people directly, she may be insulting and dismissive, but when someone engages her on questions of philosophy, or morality, or human nature, she proves herself to be extremely thoughtful and insightful, and less cynical than one would expect.

She's also a very patient person when the situation calls for it, which is a given when she's waited two hundred years for what she wants — but it's the kind of patience that comes from a place of understanding, the way a person would be patient with a child. She's not incapable of kindness, either. Only a few people have ever had her love, but she is loyal to those few, and while her personality doesn't change much on the surface, there's a certain softness to how she regards them, that patience more apparent than ever.

Shijima's entire existence centres around death. The only thing she has ever wanted is to die, but it isn't just that. When he explains their desire, Kouichi says, "We are in love with death." Having longed for it as long as they have, the two animals have a romantic obsession with mortality, often remarking on the beauty of a particular death, or complaining about going through an "ugly" death when it's one of their own. Because her only desire is death, Shijima doesn't want any attachments in life. She doesn't want to have regrets or anything that would hinder her; she values her ability to be single-minded and ruthless about her goal, willing to kill anyone who gets in her way with no regard. If it came down to it, she'd even be willing to abandon Kouichi, her existence-long partner, should he show any hesitation. She warns him as much, when she suspects he's gotten too attached to a human girl: "Don't say you feel affection for this world now, of all times."

However, deep down, Shijima is a lonely creature. Her emotional distance is not just personality, it is necessity. She never expresses it herself, but she despises her own existence and its contradictions; she cannot be a cat, and she cannot be a human. She'll never think or feel the same way as either one, and so even if she could afford to form attachments, she would, by her very nature, always be alone in the world. And in the end, she is deeply, truly, agonisingly tired. Her desire for death is not an act of self-loathing; it is the only kindness available to her.