Kotori Monou serves as the love interest and "sacrifice" that occurs in X, CLAMP's manga series about an end-of-the-world prophecy, after Kamui makes his choice.
Kotori is a classical CLAMP teenage girl, with a very slender form, long legs and arms, and very long, wavy, light brown hair.
Kotori is one of Kamui's childhood friends who meets him after a long estrangement. During their childhood, Kamui caught Kotori when she nearly fell from a tall tree, and afterward, Kamui promised her that he would always look out for her. Hearing this, her brother, Fuma, made a vow to protect both Kotori and Kamui.
A gentle and sheltered girl, raised at a shrine, Kotori hopes to one day become a designer of fabrics. Despite Kamui's apparently cold exterior when he returns to Tokyo, she continues to greet him happily and as if he hadn't changed from childhood. She doesn't request anything of Kamui, but does seem to regard him in a romantic light.
Not long after Kamui left Tokyo with his mother, Kotori's mother, Saya, died in a horrific manner that Kotori witnessed, but she blocked her memory due to the trauma it induced. Unfortunately, her memories of her mother's death return when Kamui's aunt dies in exactly the same manner, giving birth to the Divine Shinken for the prophecy. Kotori seems to lose sanity briefly before slipping into a coma, greatly worryiing both Fuma and Kamui. But in fact, she has awoken a supernatural power as a dreamseer.
In her dream, she encounters Kakyo Kazuki, another dreamseer, and they both witness scenes of two Kamuis fighting, which destroys the Earth. Kotori pleads for it to be otherwise, that she be broken instead of the planet, and Kakyo warns her that the future cannot be changed.
While Fuma sits by her comatose body, Kamui faces again the choice that he has been offered repeatedly: to either become a Dragon of Earth, to destroy mankind and save the planet, or to protect mankind and become a Dragon of Heaven. Thinking of Kotori and Fuma, Kamui decides that he wants to protect his two childhood friends. But as he re-enters Kotori's room, he finds that Fuma has now become cruel and callous, in response to being Kamui's mirror star. Fuma attacks Kamui, then snatches his sister and leaps out of the window.
When Kamui finds them, Fuma has Kotori bound to a collection of aerials, with wires cutting deeply into her body and keeping her in a crucifix position. Fuma has taken the Divine Shinken from Kamui, and uses it to kill Kotori, to Kamui's horror, and attacks Kamui again as well, only to find that Kotori's spirit is keeping him from killing Kamui at that time.
Kotori, meanwhile, is hovering in the dreamworld with Kakyo, and she asks Kakyo to give a message to both her brother and Kamui. She wants them to know that she loves them both, and that "the future is undecided". After this, she disappears into the afterlife.
There is a suggestion that had Kamui decided to become a Dragon of Earth instead of a Dragon of Heaven, he would have been the one to kill Kotori before Fuma's horrified eyes.