Kanata is from a declining magus family. His grandmother possessed Magecraft but kept to herself and eventually died when he was six. His father did not have Magic Circuits, so Kanata was raised as a regular boy, is untrained in magecraft, and does not know much about it. His father warned him not to practice magecraft in public and that magecraft does not lead to happiness. Despite the warning, he later demonstrated his slowdown magecraft at least once during elementary school to his friends such as Taka which was dismissed as just a trick.
His parents got divorced when he was in middle school putting him and his sister under their mother's custody and going by her family name. His father visits bi-yearly occasionally. He is in high school in the year 2020 (2nd year of the Reiwa Era).
He has a typical appearance of a 21st century Reiwa era Japanese male 17 year old. He has short hair. When he got sent to the past he was wearing a light colored shirt with a hoodie on top while wearing a dark backpack, he also had a dark colored pants with bright colored laced sneakers.
When he summoned Saber, command seals appeared on the back of his right hand in a shape that resembles an hourglass.
Kanata is not really interested in learning about magecraft and prefers to live a normal life. Having lived a normal life, he is unused to violence and death and quickly panics or freezes up when he sees people get killed. However, he does not hesitate to save his grandmother from Assassin instead of abandoning her and running away from certain danger.
Kanata was given a light novel by his friend Taka that claims an explosion that devastated the center of the then Imperial Capital of Tokyo and killed over 200,000 citizens 75 years ago was caused by a series of battles between supernatural beings. He fell asleep while reading it and dismisses it as just a story.
One day, his father visits and asks him to help liquidate his late grandmother's estate by detecting any Mystic Codes she may have. While examining her things such as an old photo of her, he finds a strange hourglass and uses his power of slowing down objects on it when he drops it. To his shock, the hourglass reacts to his mana and time starts moving backwards. Unable to stop it, he sees events from the day repeat themselves before the time reversal accelerates. One of the flashes of the past he sees is of a younger him talking with his grandmother. He perceives himself falling and after seeing an explosion over Tokyo blacks out.
He wakes up on a train after hearing screams. He sees a girl facing a Mysterious Officer and his Lancer. She orders him to evacuate to the rear car with the other passengers but to stay for questioning. While he can barely understand what is going on, the officer orders his Lancer to kill both of them. The girl grabs his hand and they run while she says he just appeared out of nowhere while she was being attacked by that Servant and Master. The girl is frustrated when he doesn't understand what a Heroic Spirit is even though she can tell he is a magus and briefly explains the concept. She stops and decides to summon a Servant of her own, a Saber, to counter the Lancer and tells him to keep a lookout. Just as she finishes the chant, the Lancer catches up to them and Kanata has to tackle her out of the way of his spear.
The Lancer's spear broke open Kanata's backpack and his light novel falls into the magic circle. The light novel acts as a catalyst and Saber is summoned. The girl is infuriated when the Command Spells appear on Kanata's hand instead of her own. Saber quickly kills the Lancer, which both terrifies Kanata and shocks him when he realizes she looks exactly like a character from the light novel. Saber asks him if he is her Master. Still confused, he says he is. She says their contract is established, holds his hands, and gives him a smile, stunning him with how beautiful it is.
The girl starts complaining about Kanata stealing the Servant she summoned and demands to know who he is. Suddenly, Archer appears and Kanata recognizes her from the light novel as well. Saber tells the two to run while she fights Archer. As they run, Kanata introduces himself and asks where is he and what year is it. The girl thinks he hit his head, but explains they are in the Imperial Capital in the 20th year of the Showa Era. Kanata realizes he is 75 years in the past and that the light novel depicted real events.
The Mysterious Officer tries to attack Archer from behind, but Archer shoots him in the head to kill him. Kanata is again horrified by the casual murder, causing Archer to call him a coward. He is frozen in fear as Archer tries to shoot him and the girl has to pull him out of the line of fire and then drag him away. He starts freaking out and complaining about his bizarre situation. The girl slaps him and says he needs to man up and fight if he wants to survive the Holy Grail War. He has no idea what that is, causing her to complain and briefly explain the concept.
Saber and Archer's battle ends up destroying a large portion of the train, and Saber gets thrown into the car Kanata and the girl are in. He asks if she is okay, but she tells him to stay back and not risk himself being attacked by Archer. The girl asks Saber if she has any aces up her sleeve. When she confirms this, the girl asks her to use them right away and take down Archer before the train is completely destroyed. Saber retorts that she does not take orders from her, only from Kanata, her Master. Kanata is still confused and scared, but reluctantly orders her to do whatever it takes to defeat Archer. Archer catches up to them and tries to shoot Saber, but Saber uses Lightless, Three-Stage Thrust to dodge the bullets and stab her.
When Archer is forced to retreat, Saber grabs his face and examines him because his cheek is swollen from the girl slapping him. He thinks to himself his situation is unbelievable, but he has to accept he is in the past and experiencing events from the light novel. Saber says they should leave before people come. The girl introduces herself as Tsukumo Fujimiya and says she was supposed to be Saber's Master, then asks Kanata where he came from and what his goal is. He tells himself she looks familiar, and upon hearing her name, he grabs her shoulders and stares at her face, shocking her and making her blush. He had seen her photo in his grandmother's things and has a flashback of a conversation he had with her where she asked what he wanted to be when he grew up, then said she had a dream of a bright future. He realizes Tsukumo is the past version of his grandmother.
He starts to cry because he thought he would never see his grandmother again after she had died in his time, alarming Saber and freaking out Tsukumo, but he brushes off their concerns. He tells Tsukumo he doesn't know how he got there, telling himself he'll keep their relation a secret to prevent a time paradox. As the trio salvages the train's wreckage, he finds the light novel, but it was damaged and he can't find the second half of the book. He reflects on how the book somewhat matched the events he just experienced, but he finds the Mysterious Officer's corpse and tells himself this isn't a story and he can get himself killed. Saber apologizes for not adequately protecting him from Archer and promises to win the Holy Grail for him, then tries to persuade him to leave Tsukumo behind. Offended, Tsukumo says they'll need her help to win. An air raid siren sounds. When Saber doesn't understand it, Tsukumo explains what it means and that their country is in the middle of a war, calling it a cruel joke.
Kanata and Tsukumo go around the Imperial Capital fascinating the former as he records it with his smartphone. He finds a newspaper that confirms he is in the past. They stop at a hotel somewhere and she uses drawings to explain the seven Servants, then about Command Spells and the Holy Grail. He can't believe something like the Holy Grail exists, then decides he has to win to use the wish to return to the future. Angered, she slams his head into the table and pulls out a crystal that she claims can evaporate any liquid when activated. Calling his wish ridiculous, she threatens to explode his brain and kill him unless he agrees to fight for her wish.
Saber materializes and threatens Tsukumo with her sword. Kanata tells her to stand down and says he agrees to fight for Tsukumo, but Saber insists she only fights for Kanata. He and Tsukumo then surprise Saber by recognizing her as a member of the Shinsengumi from her uniform, as Saber did not believe they would become famous. Tsukumo gives them some money and orders them to buy some regular clothes to blend in. Outside, he checks his smartphone and as expected, gets no service. He muses that he was unable to find the hourglass that brought him here, and even if he somehow convinced Tsukumo of his true identity, there is no guarantee she would be able to make it now, so his only hope of getting home is to win the Holy Grail.
Saber buys a kimono and he says it looks great, then takes her to a restaurant. Saber says she dislikes Tsukumo, so he asks her to get along as Tsukumo is important to him. Saber asks how that can be as they just met. He dodges the question by ordering ice cream. As ice cream hadn't been invented yet in Saber's time, she is delighted when she tries it and amazed when he says he eats it quite often. She then tries coffee but doesn't like its bitterness. He finds it hard to believe the vicious killer he saw last night and the cute, normal girl he sees now could be the same and asks Saber if killing bothers her.
Suddenly, soldiers from the Imperial Japanese Army walk up and point guns at him. Saber kills them all in a split second, splattering him with blood and traumatizing him. She says killing doesn't bother her because she dealt with it all the time and that people who are bothered by death are the first to die. She wipes his face with a napkin and says he has to become stronger and get used to death, because he's going to see a lot worse.
He starts to freak out and vomits, saying he cannot get used to this and cannot fight. She says it is the Servant's job to fight. He asks why she would willingly serve a loser like him, then asks what her wish is. Suddenly his hand starts to vanish due to Assassin mortally injuring Tsukumo. He checks on the first half of the novel and notices the words are starting to get blurry and the story has been changed. He becomes horrified when he read about his grandmother killed in her teens. Kanata began to realize the timeline has already start to change because of him since getting ambushed by the Japanese Army wasn’t part of the story. He realizes Tsukumo is in danger and tells Saber that they need to go back to the hotel instead of hiding just as Saber suggests they do. He begs her to help him save Tsukumo. He remembers in the original storyline, his grandmother, who was supposed to be Saber’s Master, fought against the ghost of Tosa in an alley. He tells himself that he will never get used to bloodshed, but he will fight to save his grandmother.
Saber carries him while jumping across buildings quickly heading back to the hotel before the future comes true. He contemplates how cold-hearted she is. Kanata’s condition starts to get worse as he begins to become weaker and his left hand is almost gone. He is later seen with Saber arriving back to the hotel before Assassin could finish Tsukumo off. When he saw Tsukumo’s injuries she received from Assassin, he was furious and shocked. He asks Assassin what’s he been doing to her. He later recognizes him as the ghost of Tosa. He becomes horrified when Assassin demand him to uses his Command Seals to make Saber kill herself. He becomes hesitant whether or not if he should his Command Seals on Saber to save his grandmother’s life until Tsukumo convince him to abandon her and escape. After Assassin pierce Tsukumo’s right hand through her shoulder, he starts to fade away even further as he loses most of his left face, entire arm and leg. He collapsed to the ground and struggle to sit up.
The only magecraft Kanata knows is how to slow things that he has touched with his hands, such as slowing a falling glass of water so he can pick it up before it breaks and spills.