With Teiichi's help, they begin a search for Yuuko's memories while the two stumble upon the many mysteries and ghost stories in Seikyou Academy.
Appearance and Personality
Yuuko is a tall, beautiful teenage girl with a slender figure, long black hair and walnut-brown pupils. She initially owned the old uniform of Seikyou School before it changed and she has been wearing the new uniform since, but she later changed back into the old uniform after being discovered by Teiichi.
Although her looks give off a sinister aura, she is in fact a cheerful and bubbly person. She sometimes teases Teiichi through sexual suggestions and, if Teiichi is not around, is seen roaming the school complex (often creating ghost stories as an effect). It is later revealed that Yuuko is starting to become attached to Teiichi, as he was the first person to interact with her after dying a long time ago. Worthy of note is that she does not mind to have her attractive "ghost body" seen by Teiichi, but becomes increasingly embarrassed if he does as much as pay a sight to her skeleton, claiming that it "cannot be more naked" and even calls him a pervert for doing so. While she seems to be quite proud of her body, often using it to tease Teiichi, she does have a fixation on her weight, and will try to hide it, even though she's very light.
Yuuko and Kirie, her relative, look very much alike, but with key differences. Yuuko has long hair and is busty compared to Kirie's athletic frame. The two also are very different in personalities as Yuuko is not nearly so serious as Kirie.
Plot (Manga Series)
Yuuko, The Spirit of the Mirror
In one of her random trips across the school, Yuuko stumbles upon a boy named Teiichi Niiya on an abandoned room in Seikyou Academy's Old School Building. Surprisingly, Teiichi was able to see her, and Yuuko introduces herself as the ghost of the school. To her surprise, he instantly becomes interested to know more about her, and she begins to interact with him more.
Teiichi's growing interest to know more about her eventually caused the discovery of her remains in one of the rooms of the Old School Building, and the incident becomes Yuuko's motivation to open the Paranormal Investigation Club.
The Hidden DemonDuring the first days of the Paranormal Investigation Club, Yuuko becomes involved with Teiichi in a case which is supposed to be one of the seven most famous ghost stories in the school: the story of the "Hidden Demon". According to Momoe Okonogi, the latest "victim" of the said story, she was playing the game with Yuuko-san's as the "it", and she now fears for her life now that she is unable to end the game. Yuuko appears uninterested to help Momoe out, but with Teiichi's persuasion, she decides to play along.
Yuuko dresses her part as the "Hidden Demon", while Teiichi acts as the one who will rescue Momoe from the spirit. They soon pretend that there is a purification ritual going on, complete with a fake amulet to cleanse the demon before it could reach Momoe. Fortunately, Momoe was unable to tell that everything was a fake, and with Teiichi successful and warding off the "Hidden Demon", he gained the admiration of Momoe, who later joins as a contributor to the Paranormal Investigation Club.
Spirited AwayAfter Momoe joined the Paranormal Investigation Club, Teiichi receives a letter which asks him to go to the tree in Kaede Hill for a private talk. Teiichi tried to hide this from Yuuko, but despite managing to hide the details from her, she kept her suspicions on what is going on. Her worries soon goes to a point where she looks for him throughout the school under the pouring rain. She manages to find Teiichi — and encounter the girl who met up with him. They later return immediately to avoid getting a cold because of exposure to rain.
During their stay in the school's infirmary, Yuuko slowly tries to become more intimate with Teiichi. This opportunity was interrupted by the girl from earlier, who insists that Yuuko, the girl who is now clinging to him, is a terrifying creature that will take his life if he continues to get along with her. There, Teiichi's view of Yuuko dramatically changed and, out of fear, Teiichi flees with the girl, leaving behind Yuuko, whose form is now of a maiden whose form has been corrupted by death and time.Yuuko continues to pursue the two, and this chase ends in the Paranormal Investigation Club room, where the girl, who introduced herself as Kirie Kanoe earlier, seeks Yuuko's remains. Yuuko manages to hold on to Teiichi before he could follow Kirie down the secret path inside the clubroom, and upon seeing Teiichi's reaction to her gruesome form, was close to giving up on him. However, Teiichi, admitting that he did feel fear upon seeing Yuuko's other form for the first time, decides that he will pursue her nonetheless, and is determined to see everything about her. Although elated by Teiichi's declaration, she is soon overwhelmed by embarrassment as Teiichi pushes on to investigate more on her bones on the secret path, which she deems as the moment when Teiichi sees her "most naked form".
Plot (Anime Series)
Yuuko and her Shadow
At Episode 7, Momoe wants to know more about Teiichi and suddenly getting along with him. As Yuuko notice it, she felt jealousy. Recent days, Teiichi notice that there something wrong on Yuuko. At Lunch Break, as Yuuko wants to eat at the rooftop with Teiichi. Momoe invites him to eat lunch together. Teiichi accepts it as Yuuko jealous on Momoe. At their lunch, when Momoe wants to eat him her lunch since Yuuko eats all of his Onigiri, Yuuko slap Momoe's food. As Momoe shocked, She felt clumsy on him and walk to clean her chopsticks. As Yuuko apologizes, Teiichi confirmed to himself that there something wrong on her. When Kirie and Teiichi talk about the shadow ghost. Yuuko saw them and encounter the shadow ghost which she doesn't see it because she pretended it. When Yuuko approaches Teiichi and Kirie, She heard that she doesn't felt anger and hatred to Momoe, Only jealousy. Teiichi, Kirie and Yuuko saw the shadow ghost. It say that Yuuko has no anger and hatred that keeps her beautiful and her anger and hatred gives to her shadow. As Teiichi saw Yuuko, the shadow vanished and Yuuko ran away. Teiichi chased her and they saw the Rock of Curse. As they go in the courtyard, Teiichi Noticed that the rock changed and they saw the name "Kanoe Yuko" in it. As they discussed it at the rooftop, According to Teiichi, Yuuko voluntarily became a sacrifice without hatred to the school, which this is Yuuko's past but her shadow appears and want Yuuko to remember her past. As Yuuko doesn't want to remember her past, her shadow approach her and become one of her. Teiichi didn't notice it because Yuuko seems to be happy. The next day, when Yuuko saw Teiichi's eyes, she sees something and feel depress. At Lunch Break, Momoe invites him again but Teiichi rejected it. At the Rooftop, As Teiichi finished his lunch and go back to his classroom, Yuuko feels scared because she saw her reflection in Teiichi's eyes. Her reflection is a shadow. As Teiichi stop at the stairs to call Yuuko, Yuuko stand and she pushed Teiichi at the stairs. Teiichi shocked and injured, He saw Yuuko with a raging shadow and her eyes are glowing. The next day, As Yuuko doesn't appear at Injured Teiichi. He went to Paranormal Investigation Club, He doesn't see Yuuko and look at the mirror. At the Mirror, He saw Yuuko passed by behind him. He called Yuuko. But Yuuko said that he can see her and feel relieved. As Teiichi noticed it, He said that he is Teiichi but Yuuko replied, "Sorry, But I forgotten you.". Meaning Yuuko doesn't remember Teiichi.
Eventually Teiichi tries to look for her with Kirie and Momoe behind him, and finds her on the roof of the school. Trying to make her remember he also tells her that he loves her and Teiichi accidentally falls on her touching her breasts. Yuuko soon mentions that it was just as they first met, and claims to remember Teiichi. Shadow Yuuko who is close-by mentions that she returned her the memories of Teiichi for the time being and that eventually she will serve her purpose (arguably restoring Yuuko's full memories). Momoe asks upon his confession if he loves Yuuko, and he says he does love her, to which Yuuko embraces Teiichi and claims she also loves him.
As a Ghost
The series depicts Yuuko as a ghost with traits that remain similar to a normal human. Unlike the stereotypical ghost that can fly or pass through walls, floors and ceilings, Yuuko needs to walk to her desired situation. Also, Yuuko can get hungry or be ill like a normal human would. Among those traits that Yuuko shares with ghosts is her lack of presence towards most people.
Kirie has demonstrated that how Yuuko can be seen depends on the person who perceives her. Although Yuuko is normally a girl with pale complexion, red eyes and long jet-black hair like in the eyes of Teiichi, she can take a less clear and more sinister form: a shadowy figure that resembles a silhouette. This can change depending on the person seeing Yuuko, and in Kirie's case, she saw Yuuko as a girl with gray skin, disheveled hair and a sinister look in her eyes, Kirie had also seen herself once. Another example is when the students trying to sacrifice Yuuko Kirishima see Yuuko as Akahito.
- Befitting the English title of the series, Yuuko's name literally "dusk maiden". Meanwhile, the surname "Kanoe" is derived from the 7th sign of the Chinese calendar, which originally meant "evening star" and also means "a person's age".
- Yuuko claims to weigh only 500 g (about 1 lb). However, her official weight is in fact 56.2 kg. Her height is 168 cm. Her chest measurement is 88 cm. Also, Yuuko's eyesight is 20/10 (decimal value = 2.00), and she doesn't have any hearing problems.
- There is an empty chair in class 3-B which Yuuko apparently uses when "assisting to classes". 
- In the anime series, Yuuko is attributed to autumn leaves and the sky during sunset, which both share the same fiery hues.