Yui Kiriyama/Story Plot

Spoilers below

Hito Random arc
On a night that should have been like any other, Yui awakens to find herself in an unfamiliar room. Upon inspecting her new environment, Yui realizes she is not only in the room of her abhorrent admirer, Aoki, she's in his body. Horrified, Yui hides under the bed sheets only to suddenly find herself back in her own room and body.

The next day, Yui encounters Aoki at school and the two find that they both experienced the same bizarre phenomenon. Growing suspicious of the whole thing, Aoki suggests informing their friends, and a reluctant Yui agrees. At the  Cultural Research club room, Aoki announces how he and Yui apparently switched bodies the previous night, but he is only met by skepticism. Yui, realizing with how absurd the whole idea sounds, betrays Aoki and voices her doubts as well. However, when Yui and Taichi experience the same phenomenon and announce that they have switched bodies, Yui's doubts are all but erased. Only Inaba remains skeptical. .

The following day, to Yui's distress, she finds she has once again switched bodies with Aoki and hunts down the rest of the Cultural club for help only to find Aoki has been switched into Inaba's body and Inaba, in turn, is in control of Yui's. Deciding to skip their first period classes, Yui and the others patiently wait for the phenomenon to wear off. When it does, Yui returns to her regular routine, only to randomly switch bodies with Taichi. Back in the club room, Yui angrily confronts Taichi, suspicious of why she was in the girl's bathroom of all places when they switched back. Taichi pleads innocence but their bickering is interrupted by the arrival of a being who has taken control of Gotou's body. The sentient introduces himself as Heartseed and informs the club members that he is responsible for the body-switching phenomenon, which will continue to randomly occur until he is adequate entertained. Inaba confronts Heartseed, rebelliously refusing to be anyone's entertainment, but he responds by knocking her away. In response, Yui charges at their mysterious tormentor and despite having a black belt in karate, Heartseed effortlessly blocks all of her attacks and tosses her aside. The rest of the club can only watch helplessly as Heartseed leaves.

Realizing how hopeless their situation is, the group decide to establish rules to ensure no one else learns of the bizarre phenomenon so they can continue living as normally as possible. A week later, everyone meets at Inaba's house where Yui and the others confess having failed to obey their rules, much to Inaba's frustration. Yui takes the opportunity to ask Iori why she lives alone and Yui is horrified to learn Iori is completely unconcerned about household intruders. Returning home, Iori switches bodies with Aoki and is amazed by how tall he is. Iori approaches Yui but, strangely, the petite karate girl shirks away, claiming that she's wary of Iori because she's in Aoki's body. .

The next day, several switches once again occur and upon returning to the club room, Yui (in Taichi's body) and Inaba (in Aoki's body) find Aoki (in Yui's body) and Taichi (in Inaba's body) recording cute videos of each other. Enraged, Yui seizes the boys' phones and watches their shame along with Inaba. After administering appropriate punishment, Aoki, due to his experiences while controlling Yui's body, suspects that she is afraid of menasks if Yui is afraid of men. Distressed, Yui flees the room, confirming Aoki's suspicions. Inaba pursues and calms Yui down before walking her home. Aoki would later call Yui several times, profusely apologizing for his insensitivity.

That night, Yui lays in bed, crying when suddenly she switches bodies with Taichi. She immediately calls Taichi, telling him not to worry about why she was crying, but Taichi requests they talk in person. Meeting at a park in the dead of night, Yui reveals that she suffers from androphobia, which she developed after nearly being raped in junior high. Despite being a martial arts expert, Yui felt powerless and has been terrified of men ever since. Taichi demands she let him help her and Yui reluctantly agrees. Claiming he knows a flawless technique that will neutralize any man, Taichi (while in Yui's body), punts Yui (in Taichi's body) in the crotch. Yui falls to the ground, writhing in pain only to suddenly return to her own body, leaving Taichi the one in pain. At that moment, Yui notices someone approaching and, not wanting to raise unwanted questions, flees with Taichi, but she is forced to help him to his feet due to his pain. Having escaped, Taichi compliments Yui on having been able to touch him despite her androphobia and Yui thanks Taichi for his help, her confidence restored thanks to her newly learnt weapon against men. .

The next day, Yui greets Taichi, enthusiastically patting him on the back, showing off how at ease she is around him. She announces her intentions to get back into karate and possibly try wrestling, which Taichi applauds her for.

Later, when Inaba faints, Yui worries that Heartseed is behind it, but Inaba dismisses her suspicion. With Taichi's help, Inaba confesses to her friends that her recent illness was brought on by her chronic fear and distrust of her friends. Instead of being upset, Yui and the others understand and sympathize with Inaba, and their bond with their Vice President grows ever slightly stronger. .

At Aoki's request, Yui meets with him in private and Aoki confesses his love to her. However, Yui turns him down, stating that she is still yet ready to start a relationship with a boy. Aoki understands and remains hopeful that she will one day return his feelings.

When Iori is left critically injured at a hospital due to Heartseed's intervention, Yui is traumatized, feeling useless for not being able to protect her. Suddenly, Heartseed appears himself and announces that the group can save Iori, but only if one of them exchanges minds with her, allowing their soul to die with her body. Yui is further distressed when Taichi recklessly expresses his desire to be sacrificed and by Aoki who believes Iori should be the one to die with her body. When Aoki switches bodies with Iori to inform her of her situation, Yui breaks down completely, crying tears of guilt and sorrow. Iori would later speak with everyone individually one last time before allowing herself to die with her own body. However, to everyone's surprise and relief, Iori survives her ordeal, Heartseed claiming that she was never in any real danger. Yui later helps throw Iori a welcome back party upon her return to school. .

Kizu Random arc
With normality returned to the Student Cultural Club, Yui and the others enjoy a period of peace, that is, until Yui returns to the club room with Aoki to find Inaba seducing Taichi. Freaking out, Yui demands the two get off each other and abruptly smashes the club table in half. Aoki asks what's gotten into Yui and she seemingly snaps back to reality, confused. Iori enters the room and rushes to Yui's side, tending to her wounded hand.

Returning home that day with Aoki, the two witness some boys harassing girls from their school. Yui impulsively jumps to the girls' aid, violently attacking the boys. The police soon arrive and stop Yui before placing her under arrest. Wanting to take her in for questioning, Yui is startled by her own behavior and surrenders. Aoki, however, suddenly tries to free Yui from the officer's hold and he is arrested as well.

It is only later that Yui is informed that her impulsive behavior was caused by Heartseed's latest phenomenon which forces their desires to go unrestrained, making them act on impulse. Yui and Aoki are let off with warnings, but Yui is left morbidly afraid of her impulses and hides away in her room for several days, refusing to return to school.

When her friends visit her, Yui initially refuses contact with them but eventually relents. After being questioned by Inaba, Yui reveals her fear of herself, stating that her impulses were her own and deep down, a part of her really did want to hurt others. Inaba's impulse unleashes after she becomes impatient with Yui and angrily berates her for her cowardice. Yui is reduced to tears and Inaba apologizes but Yui states Inaba meant what she said. The StuCS would later become divided over how to deal with Yui's predicament, leading to a falling out between Taichi and Aoki and between Iori and Inaba.

After a week of hiding, Yui is once again confronted by Aoki and Taichi. Aoki explains that while he loves Yui, he is also a huge pervert and how if he had his impulses unleashed, he would throw himself at Yui. Yui is disgusted, but Aoki then claims that he would never actually do that because he would be able to restrain himself through sheer force of will and states Yui can do the same. Yui is unconvinced so Aoki insists they go to a love hotel to put his theory to the test. Yui is further repulsed, but Taichi adds that now that Yui understands what it means to hurt someone, she will never let herself do it again. Yui begins to understand and agrees to return to school, but asks Aoki and Taichi to protect others from her if she loses control. At Aoki's suggestion, Yui rephrases her request to "please protect me." Aoki nobly gets down on one knee and accepts the responsibility as Yui smiles.

Later, Yui attends the class field trip Aoki, but she spends much of the time worrying about Inaba who is still bitter with Iori. Aoki, in his typical carefree fashion, insists she not worry. When the phenomenon ends, Yui returns home with the others, but worries Heartseed is far from through with them.