Yuno was born to Loyce and Ciel of House Grinberryall, the royal family of the Spade Kingdom. As an infant, Yuno is given a magic stone found in a Grand Magic Zone. Some time later, the Zogratis Siblings attack the royal castle and kill many of the royals. Knowing that Yuno will be killed if he is found, the Mage Defense Force escape with the infant, and Ralph's father carries Yuno across the Grand Magic Zone between the Spade Kingdom and the Clover Kingdom. Upon arriving at the village of Hage, the mage uses the last of his magic to deliver Yuno to the front of the church before collapsing to his death.
As an orphan, Yuno spends his childhood in the church and grows along with Asta and the other orphans. One day, during a trip home after grocery shopping with his foster family, Yuno overhears a few villagers talking about life in the Noble region of the Kingdom. After Sister Lily explained the social status within the Kingdom, Yuno hears Asta's dream to become the Magic Emperor for the first time.
Sometime later, a thug tries to take his necklace away from him so that he could sell it for the money. However, Asta steps in and forces the thug to return it. In the end, the said thug decides to leave without the necklace after the boy's rigorous attempt. Since then, Yuno stops crying and determines to take Asta's dream to be the Magic Emperor as his own as well. One night, Yuno and Asta go into the forest and stand on top of a hill while facing towards the Noble region. Asta begins to talk about their relationship as a family despite their lack of blood relation, which prompts Yuno to ask the reason behind the former's sudden interest in the topic. At that moment, they promise to treat their future comrades the same way they treat each other.
Yuno and Asta also trained from time to time to sharpen their combat abilities. The training usually consists of Yuno tries to prevent Asta from advancing with his magic. After he sees Asta fails multiple times, Yuno suggests him to stop, which is rejected by Asta. To Yuno's surprise, the latter manages to break through, which he then explains to the former that his persistence plays a significant role in his success.
Years later, Yuno still lives at the church, where he takes care of chores such as doing laundry, chopping firewood or taking care of the younger children. When he turns 15 years old, Yuno receives his grimoire during the Grimoire Acceptance Ceremony. As he learns that he has received a grimoire similar to the one possessed by the first Magic Emperor, Yuno declares his ambition to the public while brushing off Asta's declaration of rivalry. Later that day, Yuno is confronted by Revchi, who manages to snatch his grimoire and immobilizes Yuno with his magic. Once again, Asta steps in to save him, which prompts Yuno to clarify his previous statement during the ceremony and declares Asta as his rival.
Six months later, Yuno attends the Magic Knights Entrance Exam, where he manages to easily perform all of the required tasks. During the combat test, Yuno fights against Salim from a noble House Hapshass, which he finishes the moment it started. Yuno managed to impress the captains so much that all nine of them show their desires to put him in their ranks. Yuno chooses to join the Golden Dawn, as he believes that entering the strongest squad is the fastest path to become the Magic Emperor.
Before he leaves for his squad, Yuno stops Sekke Bronzazza, Asta's opponent in the exam, from harming Asta who is in the toilet. He intimidates Sekke by saying that he is not worthy of Asta and leaves without meeting his rival. As he meets his new squadmates, the young Knight is quickly being shunned by the other members due to his social standing. While he ignores their harsh treatment, Yuno begins to isolate himself as he hones his skills even further.
A few days later, Yuno is dispatched with two of his squadmates to explore the newly emerged dungeon. As they enter, Yuno immediately activates one of his spells when he sees Asta's struggle with one of the dungeon's traps. After he saves him, Yuno confirms that he has paid his debt from when Asta saved his life. Yuno and his group then meet with Asta and Noelle Silva, but Yuno decides to stand in silence as his senior, Klaus Lunettes, begins a conversation with Asta in which he believes to be a waste of time.
Not long after, Klaus ends the conversation and orders Yuno to take them to the center of the dungeon after Mimosa Vermillion located it with her spell. Along the way, Yuno warns Klaus to not underestimate Asta after hearing his condescending remark about his rival.
Not long after, they finally arrive at the gate to the center of the dungeon. Unfortunately, an ambush manages to break through Mimosa's defenses, which prompts Yuno and Klaus to prepare and fight the perpetrator. Klaus immediately asks Yuno to be his support in the fight as soon as the mage from the Diamond Kingdom, Mars, tries to attack Mimosa who has begun her healing treatment. They end up in a stalemate with both sides unable to break through the other's magic attacks.
Suddenly, Klaus asks Yuno to leave and conquer the dungeon on his own. Yuno declines at first but soon agrees after Klaus gave him a direct order. However, Yuno quickly turns back to protect Klaus from an incoming attack and declares that he will not leave his comrade behind.
After he explains himself to Klaus, Yuno releases his magical power and activates two spells at the same time. He then states that the Golden Dawn will be the one to conquer the dungeon. Unfortunately, as the fight continues, Mars manages to suppress Yuno, who is barely able to remain standing as his spells begin to vanish. Mars continues his assaults as Yuno struggles to evade every attack. Yuno tries to launch another attack, but it resulted in another failure as Mars reinforces himself with crystal-made armor.
Mars then asks Yuno to give up and admit defeat, which reminds him of the past when he trained with Asta. The memories lead to Yuno's refusal on admitting defeat as he continues to evade Mars' merciless attacks. When one of the attacks is about to hit, Asta steps in and stops it. Asta's action slightly irritates Yuno as the former saves him yet again. He then begins to argue with his rival about his circumstances with Yuno tries to cover for his struggles. The arguments stop when Asta decides to join Yuno in the fight. Soon after, the fight continues when Mars creates a number of clone puppets with his magic to attack all of them. Yuno is then stuck fighting against these puppets while Asta is able to defeat Mars.
After Klaus restrains the unconscious Mars, both the Golden Dawn and the Black Bull members enter the center of the dungeon with Asta forcefully cuts down the door. They are quickly taken by surprise with the spectacles, which they see behind the door. As soon as they enter, each member quickly explores the treasury and tries different magic tools within. Yuno then notices a scroll surrounded by wind streams as he opens it, the young Knight finds writings that he could not understand. Before he realizes it, the scroll and his grimoire begin to shine and the writings mysteriously disappear.
Yuno then hears Luck Voltia warns them to get away from the door, but Yuno fails to react in time as he is ambushed by Mars' attack. The mage of the Diamond Kingdom then manages to trap him within a crystal structure, which renders him immobile. The crystal structure also prevents him from using his grimoire as Yuno is unable to help Mimosa and Noelle from Mars' attacks. Yuno then tries to slowly break his binding with his magic as he witnesses Asta suddenly releases a water-based attack.
Unfortunately, Mars is able to suppress Asta and about to move in for the kill. Seeing this, Yuno forcefully breaks the crystals that have been binding him and quickly searches his grimoire for a spell to stop Mars. Unfortunately, he is unable to find a suitable spell, but he refuses to give up. At that moment, Yuno's surroundings suddenly become motionless and he finds Sylph has appeared by his side. She then easily defeats Mars with a single blow. Afterward, when Yuno looks back at her, she has already disappeared and similar writings, which he found within the scroll earlier, appear on a page of his grimoire. Not long after, the dungeon suddenly begins to collapse.
Seeing that the dungeon begins to collapse, Yuno quickly creates a vessel for all of them to escape. They quickly head towards the exit after they failed to fulfill Asta's request of taking Mars with them. They manage to escape from the dungeon mostly unscathed due to Luck's guidance and effort of getting rid of any falling debris with Klaus. As soon as they are outside, Yuno quickly instructs them to take Asta to a safer place for Mimosa to properly heal him. When Asta regains his consciousness, Klaus suddenly hugs him and Yuno as the nobleman acknowledges them.
After their return from the mission, Yuno immediately tries to activate the spell that he accidentally used to defeat Mars. Unfortunately, he fails as the spirit, which he saw, refuses to respond to his effort. A week after the mission's completion, Yuno along with Klaus and Mimosa travel to the Magic Knights headquarters to report about the mission. When they encounter Asta and Noelle, the five Knights then head to the designated venue together. Upon arrival, they are greeted by the Magic Emperor himself, Julius Novachrono who then examines the treasures that they took from the dungeon. While in the presence of the Magic Emperor, Yuno and Asta ask Julius about the method they should use to attain the Magic Emperor title. Julius simply explains that great results are very vital for the acknowledgment.
Afterward, Yuno is invited to attend a War Merits Conferment Ceremony that honors several Magic Knights that have produced the most results. At the end of the ceremony, Yuno and his fellow Knights who explored the dungeon with him, are scrutinized during the celebratory banquet, but Yuno decides to remain silent. While he watches Asta confronts the honored Knights, Yuno becomes curious when one of those Knights, Leopold Vermillion, declares Asta as his rival. Mimosa then explains to him that the two brothers from the Crimson Lion squad are her cousins.
Not long after, someone suddenly enters the banquet hall and reveals that the Royal Capital is under attack. Yuno then joins his colleagues as they figure out a counterattack strategy. In the end, Yuno leaves along with Alecdora Sandler and Mimosa to the Northwest District of the Royal Capital. As they arrive, an army of corpses quickly surrounds them from every direction. Yuno then proceeds to defeat every corpse that he sees while Mimosa is healing the injured.
After all of the corpses are defeated, Yuno's grimoire begins to shine and a Spatial Magic spell activates beneath their feet. At that moment, Sylph, of her own volition, lifts Yuno up into the air, saving him from being transported a considerable distance away from the Royal Capital. With the Knights gone, Catherine appears and begins to attack the citizens, and Yuno quickly engages in a fight against her.
As the fight begins, Yuno tries to find the reason behind the invasion but Catherine only reveals that their attack is a part of an assassination mission. She then quickly begins to outmatch him with her curse magic spell that slowly renders the latter's senses obsolete. During his struggle to land even a single attack against her, Yuno starts to reminisce his experiences since obtaining his grimoire where he is disappointed with his own slow progress of honing his skills. In the end, Catherine's spell finally takes all of his senses away from him. However, at that moment, Yuno's latent ability to sense mana is suddenly awakened, which allows him to summon Sylph, who has been lying within his grimoire. Using Sylph as his medium, Yuno launches an enormous attack towards his opponent.
Using his new ability to sense mana, Yuno realizes that Catherine managed to survive his attack. The young Knight immediately moves towards her position in one of the towers of the city. As he is closing in, Yuno began to sense a sinister magical power is brewing inside the tower before his opponent is sent flying away from the said tower. When he arrives, Yuno encounters Charmy Pappitson in which after seeing her affiliation with the Black Bull squad, he believes that the sinister magical power belonged to her. Subsequently, Yuno passes out after he exhausted all of his mana from fighting the mysterious mage.
Later on, as the invasion is over, Yuno strolls around the Royal Capital with Klaus and Mimosa. They then encounter Asta and the other Black Bull mages, who are about to depart from the city. Yuno then launches an attack towards them, which turns into words of farewell to Asta. He then leaves without saying anything else to his rival.
Months later, an army from the Diamond Kingdom attacks Kiten. Fourteen members of the Golden Dawn squad arrive to repel the invaders. Yuno confronts Broccos, one of the Eight Shining Generals, and defeats his giant boar and his men with a single Tornado Fang. Sylph accuses Yuno of trying to impress someone else, and the two bicker.
Broccos wants to take on Yuno, but Ragus swoops in and questions if Yuno can defend himself and the citizens. With Sylph's help, Yuno counters the Lightning General's attack with Gale White Bow, piercing the general's barrier. Yuno then returns Ragus' question, asking if the general can protect his own men. Ragus and Broccos argue who will get to fight Yuno, while Sylph claims that he is hers. After William's Great Tree Misteltein defeats most of the Diamond soldiers, Broccos leaves the fight, and Yuno and Ragus continue, both flying up into the air over Kiten. After exchanging spells, Yuno begins overwhelming Ragus and defeats the general with a giant trident, which knocks him down into a building.
Yuno notices Asta below and lands in front of him. Smiling, Yuno reaffirms their rivalry. Yuno and Asta exchange insults, which makes Sylph jealous. Yuno then takes a pastry that Charmy offers him, which also makes Sylph jealous. Yuno later watches as the Black Bulls fight Yagos, and afterward catches Asta with a wind stream.
When the Diamond Kingdom forces retreat, Yuno bids farewell to Asta as Sylph and Charmy bicker. After the Black Bulls leave, Langris suggests that Yuno should choose his friends more carefully, but Yuno states that he is proud of Asta and that Asta is his rival. Langris laughs and asks for what they are competing, to which Yuno replies that they are both aiming to be the Magic Emperor. Langris laughs and says that commoners must not feel embarrassment, but also says he would expect nothing less from the peasant chosen by a four-leaf grimoire. Sylph gets angry at him, but Yuno calmly points out there is no rule stating commoners cannot become the Magic Emperor. He then deadpans that first, he will become the Captain of the Golden Dawn. Langris angrily notes that Yuno is ignoring him, the vice-captain.
Weeks later, at the Star Awards Festival, Julius announces that the Golden Dawn is the top-ranking squad and calls Yuno to the stage as he contributed the most stars. Asta is thrown onstage as the Black Bull representative and the two rookies greet each other. When the crowd doubts the boys' strength, Yuno has Sylph release her full power and fires an arrow at Asta, who cuts it. The resulting streams of wind blow through the audience, which impresses them. Julius takes that moment to rally the citizens behind the two boys. Yuno and Asta marvel at how far they have reached, while the crowd cheers for them.
Yuno and Asta are left speechless but unimpressed when Augustus Kira Clover XIII takes the stage. The king announces the Royal Knights Selection Exam, but Asta questions why the king is the one choosing the Knights. Yuno and Asta openly discuss the king and his lack of achievements, so Augustus orders their execution. Julius steps in and talks the king down. Afterward, Julius talks alone with Yuno and Asta and warns them not to be arrogant in the coming exams.
As the boys make their way down the tower stairs, they witness Mereoleona Vermillion berate the Crimson Lion squad. They overhear Mereoleona mention training in a hot spring, which Yuno considers easy while Asta considers it fun. Overhearing them, Mereoleona grabs both of their heads and forces them to join the training. She carries them to the Ultime-Volcano Mountain Trail after also picking up Yami Sukehiro, Charlotte Roselei, and Noelle. Leopold challenges Yuno and declares that they are rivals because they are both Asta's rivals, but Yuno does not care.
Mereoleona forces everyone onto the path, and most struggle to withstand the heat. After watching Yami and Charlotte use Mana Skin, Yuno concentrates and creates his own protective barrier. He then flies on ahead, taunting Asta, and destroys the falling rocks with whirlwinds. As he is reaching the peak, Yuno spots Asta flying after him and covered in Anti Magic. Yuno lands and watches Asta fly past him and be taken out by Mereoleona.
That night, when the volcano crater fills with water, Yuno joins the men on their side of the hot spring. Leopold heats up the water in an attempt to break Yuno's cool demeanor, while Yuno uses his Wind Magic to cool the air around him. Yami interrupts and suggests that they all peek on the women, which Yuno refuses to do. Yami threatens Yuno, and Asta comes to his brother's defense, pointing out that Yuno has only ever bathed with men, which frustrates Yuno because it could be misunderstood. For the rest of the week, Yuno continues training with Mana Skin and Slyph.
As the Knights gather for the Royal Knights Selection Exam, Yuno and Asta greet each other and bicker with Leopold about who will win a spot. After listening to Augustus and Julius explain the exam, Yuno is placed on Team P with Noelle and En Ringard.
Before Team P's first match, Yuno and Noelle are bickering when Solid interrupts them. As the match begins, Yuno and Noelle disagree on who will lead the attack. The conversation is cut short when Yuno senses Team O rapidly approaching. Yuno attacks them while Noelle raises a defense, but when Alecdora uses his sand to absorb the water, Team P is forced to split up. Yuno flies off with Noelle and the crystal, and Alecdora chases after them. Noelle convinces Yuno to let her go after Team O's crystal by herself, so he creates a small Heavenly Wind Ark for her. He then turns and confronts Alecdora.
Yuno turns down Sylph's offer to help and destroys Alecdora's sand warrior by creating a Towering Tornado inside of it. Afterward, Yuno criticizes the defeated Alecdora, rejoins the others back on the platform, accepts a dessert from Charmy, which causes her to faint.
Later, after the Black Bulls stop Langris from killing Finral, the vice-captain tries to attack Asta, and Yuno senses that something is wrong. After Team B vs. Team G ends in a draw, Yuno defeats Team M by himself.
During the final match, Yuno and Sylph fight Rill Boismortier, while Nolle and En fight Nils Ragus and Ruben Chagar. Yuno initially struggles as Rill seals away any attacks within paintings. Yuno decides to show off his Spirit Dive, absorbing Sylph and greatly increasing his magic power. He unleashes his Spirit Storm, which Rill matches with Phantom Dragon Vouivre's Shout. The two Knights grow more and more excited until Rill accidentally shatters his own crystal. Team P are declared the victors of the match and the tournament.
Several days after the exam, Yuno and the others selected to be Royal Knights all assemble in the Royal Capital and are placed under the command of Mereoleona. Yuno changes into the new squad robes and reminds Asta, who is spacing out, of their competition for Magic Emperor.
After the squad travels to the Gravito Rock Zone, Mereoleona explains the situation and divides the squad into teams. Yuno infiltrates the dungeon with Mimosa, Klaus, and Hamon. As the team progresses, Yuno hears something from further ahead. After defeating three more mages by himself, Yuno reaches a stair leading to the source of the sound, the central chamber. There the team finds a man floating in a large sphere of magic. At the same time, Patolli finishes placing the magic stones in the sephirot. Yuno, Klaus, and Hamon begin glowing and are possessed by elf spirits.
Yuno stands by as Mimosa is beaten and restrained by her possessed teammates. Rhya drops Asta in the room, and the boy tries to free Mimosa but is attacked by Klaus and Hamon. Asta reaffirms his dream to become the Magic Emperor, which rouses Yuno to his senses. Yuno then defends Asta from Klaus and Hamon's combined attack and counters that he will claim that title.