Early LifeKurumi was once an ordinary human before becoming a Spirit. She grew up as the daughter of a rich family and was beloved by her parents. However, one day while returning home she was attacked by a monster. She was saved when a girl wearing a dress made of light killed the monster. The girl introduced herself as Mio Takamiya and claimed herself to be an "ally of justice". She told Kurumi that the monster was called a Spirit and asked her if she wanted a power like hers to help her fight them. Wanting to protect her family and friends, Kurumi accepted and was given the Sephira Crystal containing Zafkiel. Afterwards, she bonded with it, unknowingly turning her into a Spirit herself.
Working together with Mio, Kurumi began hunting down Spirits. However, one day after killing a Spirit, Kurumi left Mio with the task of cleaning up the it's body. Kurumi then left, but took a wrong turn and returned to the scene. Now, instead of a monster, Kurumi found her best friend Sawa lying dead as Mio holding a red Sephira Crystal. Realizing Sawa was the Spirit and she had killed her, Kurumi started to inverse. However, before she completely transformed, she used her fourth bullet and reversed time. Mio then revealed the truth; she was having the Sephira Crystals bond with humans, turning them into monsters, and then kill the host in order to slowly purify the Crystals. Mio claimed that she intended to entrust the Sephira Crystals to someone before causing Kurumi to black out. Kurumi woke up in a giant crater after causing a spacequake with no recollection of who she was or where she came from. She eventually used her tenth bullet on herself to regain her memories. Afterwards, Kurumi made up her mind to use her twelfth bullet to travel back in time to kill Mio and prevent the existence of Spirits from ever happening.
At some point, using her ability to make clones of herself, Kurumi had created a massive information network. In order to gain enough time to use the Twelfth Bullet, she and her clones began to prey on humans, taking many lives in the process. However, the many lives she had taken attracted the attention of DEM, who sent Mana Takamiya after her. They fought many battles, during which Mana had always killed her. However, unbeknownst to Mana, she was just killing Kurumi's clones. Much later, <Phantom> appeared before Kurumi at some unknown point in time and told her about Shido Itsuka, along with the Spirit mana sealed inside his body. Having nothing to lose, Kurumi infiltrated Raizen High School through unknown means to confirm if this story was true.
The Black VisitorsKurumi transfers into Shido's class revealing herself to be a Spirit to get closer with Shido. During her time touring the school with Shido, who was oblivious of the fact that they'd been followed by Origami Tobiichi and Tohka Yatogami. At that time, Shido is attempting to seduce Kurumi, but she is also attempting to do the same thing to Shido. After school, Kurumi kills three delinquents that she met while walking along the streets and is then confronted by Mana Takamiya. Mana then runs into Shido later on that day. Taking her to his house, what Mana shares about herself leads to a quarrel between her and Kotori and when she was asked by Shido where she works, she ultimately leaves everyone with more questions than answers. During school the next day, Shido finds out that Kurumi was killed during her confrontation with Mana yet she appeared at school. Origami questions Kurumi in a secluded place and finds out that Kurumi is ultimately after Shido.
Triple Frenzy TuneShido invites Kurumi out but is forced on a polygamous date when Tohka seduces him and Origami forces her plans upon him for a date. Shido is unable to deny any of them as Tohka would be heartbroken, Origami would be suspicious and his plans to seal Kurumi depend on the date. With their dates occurring around the same time and their entertainment venues located rather close to each other, Ratatoskr assists Shido by teleporting him to each girl's location while monitoring their emotional levels.
After Shido leaves Kurumi, she finds some boys shooting at a stray cat and convinces them to let her play with them. Ratatoskr loses sight of Kurumi as Origami Tobiichi and Tohka run into each other. After they both proclaim they are trying to find Shido for their date, Origami runs off concerned there may be another. Shido returns to look for Kurumi but finds blood, body parts, and Kurumi killing a man. As she holds Shido within her clutches, Mana Takamiya intervenes wearing her CR-Unit.
Ranging NightmareMana Takamiya kills Kurumi and explains everything to Shido. After that he is forced away, he then avoids Origami and Tohka after running into them because of seeing the death Kurumi caused. Tohka finds out the reason for Shido's behavior and continues her date with him to try to cheer him up. After gaining some insight to Kurumi, the next day Shido declares to Kurumi that he'll save her.
Kurumi goes to the school rooftop while encasing the school in her field which eats the time of people therefore making them faint to dissuade Shido from trying to save her. At the same time, Mana is currently confronting Kotori about Ratatoskr and attempting to use it as leverage against Kotori so she'll release Shido from the potential danger he's in. While Kurumi is threatening the school and the town, Origami and Tohka are engaging in battles with other copies of Kurumi. Shido convinces Kurumi only for her to be killed by another Kurumi. As Tohka and Origami show up, it's revealed that the hands in Kurumi's shadow are actually the hands of other copies of herself. Kurumi takes everyone as hostages and attempts to summon a spacequake only for it to be blown away. Kotori appears, explaining the cancelling of the spacequake while in her Spirit form. She has that time taken back her Spirit powers from Shido temporarily to fight Kurumi.
Spirit of FlameKurumi and Kotori started fighting after a short conversation. Kurumi used one of her skills which is her Seventh Bullet, Zayin, to make Kotori stay still, creates copies of herself, and shoots Kotori a few times.
Kotori fell over after Kurumi's last shot but Kotori's healing skill enables her to not die and to heal from her wounds. Then, the shocked Kurumi sent her copies to kill Shido, but he was pushed away by Kotori and the copies were killed. In the heat of the fight, Kurumi used one of her skills to inhibit Kotori but it only worked for a while. Kotori used her weapon to shoot Kurumi's angel after the frightened Kurumi summoned her copies to shield her. Shido immediately stood in front of Kurumi to shield her, knowing Kotori is no longer herself when he tries to reason out to her not to kill Kurumi. After the shot was launched, Kotori suddenly regained consciousness and changed the direction of the shot hence saving Kurumi.
Things You Can't Give UpKurumi appears only at the end of the episode. After Kurumi have fled the battle against Kotori, she disappeared for 3 months in a row. However, Kurumi was still in Tenguu City. During these 3 months, she killed many people, stealing their lifespan and devouring them to mutton her hunger. Kurumi appeared in the last episode of Season 1 (Volume 4) as she had eaten else to sunset. In these events, a greater evil would appear. Kurumi also would have to unite with the heroes to fight against DEM Industries and Isaac Westcott.
Miku TruthKurumi and Shido decided the best course of action is to convince Miku to help leave them alone as they attempt to save Tohka from DEM. Along the way to Miku’s home, Kurumi relentlessly teases Shido about both “Shiori” and the size of Miku’s bra. However, the teasing was cut short, as they found a CD and a mysterious photo. Kurumi uses the Tenth Bullet -Yud- on the photo and CDs to peek into Miku's past, but the sound of Miku's Army Breaker Diva Gabriel interrupts Kurumi before she can explain to Shido about Miku's oddity.
Knowing that soon everyone in the area will be after them, Shido and Kurumi decide to confront Miku directly.
As Kurumi and Shido stand against thousands of people brainwashed by Miku, Kurumi summons her City of Devouring Time to take care of the mindless masses. However, Miku's Army Breaker Diva manages to give the people enough strength to overcome Kurumi's City of Devouring Time. Surprised, Miku boasts that her Army Breaker Diva isn't limited to enchanting people. Not one to be easily impressed, Kurumi and promptly summons her past selves (clones). The area immediately becomes engulfed in darkness as the battle begins.
With Yoshino and the Yamai twins busy fighting against the myriads of Kurumi selves, Shido is quickly taken to where Miku is by one of the past selves under the acceleration effect of the First Bullet Aleph. Kurumi drags Shido and Miku into her shadow so that the two can speak privately. However, the strain of fighting three Spirits and maintaining the space proves too much for Kurumi, who resorts to using the Second Bullet Bet to slow down time for their escape. Afterwards, Kurumi receives information about Tohka’s whereabouts from her other selves. She requests a pat on the head from Shido as a joke. Kurumi tells a flustered Shido that she is only joking and reveals Tohka's location; the DEM Industries Building No.1 of Japan Branch. However, as they arrive at DEM’s footsteps, Isaac Westcott actives spacequake alarm and send thousands of his of his soldier to kill Kurumi and her army. However, Mana appears and attacks Kurumi. Seeing her chance to move on her own, she decided to leave Shido to Mana.
During the aftermath of the battle, Kurumi remarked that she doesn't found her main target, the Second Spirit, the Spirit captured by DEM and knows the identity of the First Spirit.
Origami finds Kurumi and requests to be sent to the past with the power of Kurumi's Twelfth Bullet <Yud Bet>. Kurumi jokingly asks Origami if she wanted to go back so that she can see Shido when he was an innocent child, to which Origami replies that she wishes to go back five years ago to kill the Spirit that murdered her parents, thus changing history. Sympathizing with Origami's desire to alter the past, Kurumi eventually agrees to send Origami back in time. However, she tells Origami that she is using the former AST wizard as a test subject for the Twelfth Bullet and that she will use Origami's spiritual energy to power the time travel. Origami remains adamant and assures Kurumi that she is ready to pay the price as long as she is sent back before the incident which occurred five years ago. Then, Kurumi summons Zafkiel and shoots Origami with the Twelfth Bullet.
After seeing Origami tap into her inverse form, Kurumi takes the chance to talk to Shido. Kurumi tells him that everything he did will become meaningless once Origami went into her inverse form. She then proceeds to shoot Shido with the Ninth Bullet alongside the Twelfth Bullet, sending him to five years in the past to find out the reason for Origami
After Shido realizes that he had traveled back in time, he suddenly hears Kurumi's voice in his head. He scans his surroundings to search for Kurumi, but she tells him that she is in a different "time". Kurumi explains that she has sent Shido five years into the past using the Twelfth Bullet, <Yud Bet>, as well as the Ninth Bullet, <Tet>, which allows her to connect –communicate telepathically and share senses– with people in a different time. Shido argues that he needs to return to the present to help Tohka and the others, but Kurumi tells him about how she sent Origami to the past before she returned as an Inverse Spirit. Kurumi says she wants proof that history can be changed. She gets a little sentimental and says she's talked too much. She then urges Shido to hurry and find out what caused Origami to go Inverse.
After watching the events of five years ago unfold, Kurumi concludes that by sending Origami and Shido back in time, she has helped to create the current timeline. She concludes that the best course of action is to send Shido back in time again to change history. However, in an attempt to save Spirit mana, the action will be done by the Kurumi of five years ago. Kurumi says that five years ago she was near where the fire broke out. Shido asks if she had met him at that time, but Kurumi denies this and says she was just there to see the flame, as another Spirit could have very well caused a disaster on such a scale. Kurumi says she can guarantee that she was around the fire then, but she did not meet Shido. However, if such a meeting occurred, history would be altered.
Past-Kurumi, who is wearing an eye-patch, asks what business Shido has in a place like this, which prompts him to ask her bluntly for help. Eye-patch Kurumi is surprised that Shido knows her name and warns him not to move. He tries to tell her that he was sent here by the Kurumi from five years later. Present-Kurumi tells Shido that they don't have a lot of time and asks him to touch the eye-patch Kurumi. Shido says it's fine if she keeps pointing the gun at him, but he'd like her to hold his hand. Eye-patch Kurumi cautiously complies, and Present-Kurumi quickly explains the situation. After a moment of silence, eye-patch Kurumi agrees to shoot Shido with the Twelfth Bullet. Before Shido disappears, eye-patch Kurumi wishes him good luck, and Shido tells her that he thinks the eye-patch suits her well. Present-Kurumi lets out a choking sound upon hearing this while the other Kurumi thanks Shido for the compliment and bids him farewell until they meet again five years later.
During the second time jump, Kurumi listens in on Shido’s conversation with Phantom. She wonders if Shido knows who Phantom is. Regardless, Phantom refuses to give answers to Shido on the basis that Kurumi is eavesdropping on their conversation.After Origami’s appearance in the new timeline, Kurumi reappears before Shido and reveals that she has also retained memories of the original world, and she knows that Origami has become a Spirit, but she is uncertain as to what event could have caused Origami to become a Spirit in this world. Kurumi changes into her Astral Dress and says that she can, however, use the Tenth Bullet <Yud> on Origami to find answers. Shido asks Kurumi for her help.
However, the instant that Origami sees Kurumi, she automatically assumes her Inverse form. Origami calls out the name of her Demon King, Devil of Salvation <Satan>, and attacks Kurumi and Shido. Kurumi leaps into air and shoots at Origami, but the shot is easily blocked by Origami's "feathers", while the defenseless Kurumi is torn apart by Origami's attacks. Shido screams out Kurumi's name and turns to Origami, only to be surprised by how her "feathers" and Astral Dress have vanished, leaving Origami in her school uniform. Shido tries to make sense of the events before him and is more confused when Origami asks him what she's doing here. Origami asks Shido if she's had a black out again and says she's been losing consciousness since a while ago. She thinks she's probably suffering from anemia and leaves after asking Shido if he has read the note she's given him.
Kurumi shows up again and tells him that it was only a clone created from the Eight Bullet, <Het>, whom Origami had torn apart. She tells him not to worry but says that it will be difficult to use the Tenth Bullet on Origami like this. Shido wonders if he made a mistake, but Kurumi tells him that their current situation is not as bad compared to what took place in the original world. Shido understands what Kurumi is saying, but he can't agree with her because he wants to know what happened to Origami. Kurumi says she's also interested in how altering past events can change the world, but tells Shido that she's not that softhearted and will be taking extra fees for any favors from now on. She bids Shido farewell and disappears into the shadows.
After Isaac Westcott ordered his forces to deliver his secret Spirit known as <Material A>, who is actually Nia Honjou whom was kidnapped by DEM and kept by DEM for 5 years under daily torture, Kurumi shows up at the Neryl Island where the DEM is about to prepare the transport to send Nia Honjou to Japan. When she looked close, she noticed <Material A> in a giant cage and is being prepared to be transported from Neryl Island to DEM’s Japanese headquarters, Kurumi launches a swarm of her clones to retrieve the captured Spirit, causing an intense bloody battle between DEM forces and Kurumi's army of clones. However, at that instant, all of her clones are swiftly defeated by the new Adeptus 2, Artemisia Bell Ashcroft.
Later, it was revealed the plane carrying Nia fell when she reacted to Shido's energy. After Shido’s condition stabilized, Kurumi emerges from the wreckage of the transport aircraft. She uses the tenth bullet <Yud> to recall the memories of the plane before it crashed. She witnesses a scene where the airplane trembled as a pillar of light erupted from the distance. She concludes that the event has something to do with Shido, and is grateful that she can retrieve the Second Spirit without sacrificing a lot of her clones. However, much to her surprise, the Second Spirit already escaped.