Yoichi Isagi is a teenager of slightly above-average height with a muscular build, which becomes more defined as he develops through intense training. He has short, dark blue hair with a distinct V-shaped fringe framing his deep blue eyes.

In his Ichinan High School days, Isagi sported a casual yet tidy look, wearing an unbuttoned blazer over a white undershirt paired with a striped tie. His football jersey and gym uniform were light-colored with black stripes, matching the school’s athletic theme.

During his time at Blue Lock, Isagi dons the standard-issue body suit, a sleek black outfit with striking blue accents, along with the matching tracksuit. In the First Selection, he represented Team Z wearing the blue #11 jersey and gray-capped cleats. For the Second Selection, Isagi initially wore Team White’s #15 jersey before switching to red. Later, during the Blue Lock Eleven tryouts, he wore Team A’s black #15 jersey, marking a progression in his journey.

In the high-stakes match against Japan’s U-20 team, Isagi’s official Blue Lock uniform prominently displayed the #11, resembling the one featured in the first cover spread but notably lacking the Japan flag.

As a regular for Bastard München in the Neo Egoist League, Isagi now wears their signature red and black uniform with gold stripes, proudly bearing the #11 jersey.

Yoichi Isagi is an easygoing and cheerful individual with a friendly demeanor, though his simple and innocent habits occasionally irritate those around him. He often avoids petty squabbles among the Blue Lock competitors, striving to act as a mediator between friends and rivals. However, at the start of his journey in Blue Lock, Isagi struggled with self-doubt. Ranked near the bottom of the initial player list, he faced internal conflicts about his football ideology, shaped by his high school experience, which clashed with Blue Lock‘s philosophy of ego-driven play.

As time progresses, Isagi develops a more assertive and confident persona, both on and off the field. His growth becomes evident as he emerges as a cornerstone of Team Z, earning the respect of his peers, including some of Blue Lock‘s most dominant and assertive personalities. By the Third Selection, Isagi displays enough charisma and confidence to openly engage with Rin Itoshi, one of the most talented yet challenging players in the program.

Initially unsure how to embrace Blue Lock‘s ego-centric philosophy, Isagi’s transformation begins with Team Z’s first victory. The thrill of winning and the stark reality of survival in the program ignite a ruthless streak within him. He learns to prioritize his goals over the dreams of others, adapting his mindset to score and progress. On the field, Isagi is calculated and opportunistic, constantly seeking the “chemical reactions” that maximize team synergy while staying a step ahead of opponents. Despite his hunger to win and assert his dominance as the best player, he values his teammates’ strengths and collaborates effectively to achieve his goals.

A pivotal aspect of Isagi’s development is his rivalry with Rin Itoshi. After losing to Rin, Isagi becomes determined to surpass him, emulating Rin’s habits and mindset to close the gap in their abilities. For Isagi, outpacing Rin represents a crucial milestone in his quest to become the world’s best striker. Despite his growing confidence, Isagi is not immune to nerves, which occasionally surface before critical matches, such as the First and Third Selections or the Japan U-20 match. Nevertheless, he consistently overcomes these moments, channeling his ego to stake his claim as one of Blue Lock‘s top players.

Isagi’s evolution extends beyond the field. He rejects dismissive remarks about his achievements being mere “luck,” as seen in his encounter with Tada, a former teammate. Such comments only fuel his determination to prove the effort and sacrifices he has made to reach his current level.

By the time of the Neo Egoist League, Isagi’s ego becomes more pronounced. He feels deeply insulted when teammates like Yukimiya question his decisions, leading to heated confrontations, such as a near fight in the locker room. Similarly, during the Bastard München vs. Manshine City match, he is visibly frustrated when Kunigami intercepts a scoring opportunity Isagi meticulously planned, and when Kaiser mocks him as a mere playmaker. These moments reveal Isagi’s growing resolve to assert his individualism and ego.

Notably, Isagi’s perspective on football aligns closely with Jinpachi Ego’s philosophy—a shared obsessive desire to win. This similarity becomes evident as Isagi starts displaying Ego’s signature devilish grin during moments of intense focus. A turning point occurs during Bastard München’s match against Paris X Gen, when Isagi learns that his idol, Noel Noa, has been using him as a stepping stone for Kaiser. This revelation awakens a new level of rage and determination in Isagi, fueling his drive to dismantle the expectations placed upon him and assert his dominance over everyone who doubts him.

Isagi grew up idolizing Noel Noa, a French national team forward, and aspired to become Japan’s National Ace Striker. His passion for football led him to join Ichinan High School, where he played as the forward for the school’s football team. In his second year, Isagi found himself in a crucial match against Matsukaze Kokuo High during the Saitama Prefecture Finals, with Kira standing as one of the opposing team’s key players.

During the game, Isagi showcased his offensive prowess, effortlessly bypassing defenders and charging down the field with ease. His thoughts were solely focused on reaching the Nationals, and as he approached the goal, he found himself in a perfect scoring position. However, one of his teammates called for a pass, despite the clear opportunity for Isagi to take the shot himself. Isagi, adhering to his team-oriented mindset, passed the ball to his teammate. Unfortunately, the shot was missed, and his team lost their chance to compete at the Nationals.

After the game, the team gathered around their coach before each player left. On his way home, Isagi replayed the scenario in his mind, imagining what would have happened if he had taken the shot himself. In this mental picture, Isagi saw himself scoring the goal and leading his team to victory. This moment of self-realization made him question his decision to pass. He came to understand that, in that situation, being selfish might have been the right choice.

However, this revelation conflicted with Isagi’s core beliefs about football. Raised in a culture that values teamwork and collective effort, he struggled to reconcile the idea of individual glory with his understanding of the sport. His frustration and confusion boiled over, causing him to yell in anger and cry in solitude.

Upon returning home, Isagi shared the loss with his parents, and his mother handed him a letter informing him of an invitation to a mysterious “Player Improvement Project.” The news left Isagi feeling both excited and uncertain about what lay ahead, setting the stage for his next phase in football.

Meguru Bachira

Isagi first meets Bachira when Kunigami tells him to watch where he’s going, only to discover Bachira sleeping on the floor. Initially unsettled by Bachira’s eccentricity, Isagi quickly bonds with him after their first match against Team X. Over time, they train together often, and Bachira expresses his unwavering belief in Isagi, passing to him consistently. He hints that he sees a “monster” within Isagi, akin to the one he recognizes in himself. Before their match against Team V, Bachira tells Isagi that he’d feel lonely without him if they lost, and Isagi agrees. Bachira might be Isagi’s first real friend since his struggles in Blue Lock, though he still connects with other strong players like Itoshi Rin.

In the Second Selection, Bachira is briefly stolen by Rin’s team after their loss, and Isagi promises to reclaim him. Though Isagi barely fails in that pursuit, their friendship remains intact, and they continue playing football together. In the Third Selection, they no longer play official games together but both make the Blue Lock Eleven and face the Japan U-20 team. They share a joyful moment after the match, celebrating on the field and indirectly causing their parents to meet. By the time of the Neo Egoist League, Bachira is a close friend whom Isagi supports, offering sound advice as they both strive to become the best strikers in the world.

Rensuke Kunigami

Kunigami first crosses paths with Isagi when he accidentally throws his shirt at him. Isagi is immediately impressed by Kunigami’s physical prowess and strong moral compass. Their bond strengthens after Isagi trusts Kunigami to score the last point in their game against Team X. Though they part ways after the First Selection, they meet again during the Second Selection, where they face each other in a 3v3 Rivalry Battle. Despite Isagi’s team winning, he does not choose Kunigami, which Kunigami respects. This loss, however, stays with him, and Isagi is surprised when Kunigami is eliminated in the Third Selection by Ryusei Shidou.

Kunigami returns as part of the Wild Card, now colder and more serious. Though Isagi is the only person Kunigami speaks to in the Germany Stratum, their interactions are often rude and condescending. Despite the tension, Isagi does not feel threatened by Kunigami’s presence. After their game against Manshine City, Isagi seeks Kunigami’s advice on improvement. Though Kunigami is reluctant at first, he agrees to play a 2v2 game with Isagi, Bachira, and Chigiri, rekindling their camaraderie.

Hyoma Chigiri

Initially indifferent, Isagi and Chigiri’s first significant interaction happens after their match against Team Y, when Chigiri helps Isagi understand spatial awareness. Later, when Team Z faces Team W, Chigiri recognizes Isagi’s determination and joins in the effort to win, solidifying their bond. As teammates, they develop excellent chemistry, with Isagi relying on Chigiri’s speed and Chigiri trusting Isagi’s ability to read the game. Outside the field, they enjoy a friendly relationship, even spending time together bowling after the Japan U-20 match.

Asahi Naruhaya

Isagi and Naruhaya share a relatively positive relationship within Team Z. However, their rivalry intensifies during the Second Selection when Naruhaya, believing Isagi to be mediocre, is eliminated. Despite their differences, Naruhaya wishes Isagi luck and encourages him to continue winning.

Gurimu Igarashi

Igarashi immediately bonds with Isagi, sharing his background and motivations for joining Blue Lock. Though Igarashi initially targets Isagi in the game of tag, Isagi later chooses not to exploit him when he notices Igarashi’s injury. Both players survive the Entrance Exam, and they are surprised when Ryosuke Kira dismisses them as weak players despite their survival.

Shoei Baro (Team X)

Baro is the first true striker Isagi faces in Blue Lock, and their competitive relationship forms the core of their interactions. Isagi seeks Baro’s advice but quickly grows determined to surpass him. They engage in multiple clashes, often trying to outdo one another. Though they argue and sometimes hinder each other, they respect each other’s abilities, viewing each other as significant rivals.

Ikki Niko (Team Y)

Niko’s spatial awareness skill leaves a strong impression on Isagi, who learns to analyze the field more effectively. Their rivalry escalates when Isagi wins their match, and Niko vows to improve as a striker. Despite their competitive relationship, they respect each other and remain friendly. Niko even credits Isagi for helping him rediscover his passion for football.

Seishiro Nagi (Team V)

Isagi and Nagi first interact during the First Selection, where Nagi’s ball control impresses Isagi. They quickly develop a remarkable chemistry on the field, with Nagi leveraging his trapping skills and Isagi creating opportunities. After their loss to Rin’s Team Red, Nagi promises to catch up with Isagi, and they meet again during the Third Selection. Their rivalry intensifies during the Neo Egoist League, where Nagi scores an incredible goal against Isagi but is ultimately shut down by him. Despite the rivalry, Nagi’s respect for Isagi grows, and he continues to push himself to improve.

Reo Mikage (Team V)

Reo’s initial rivalry with Isagi stems from jealousy over Nagi’s decision to join Isagi’s team. This evolves into a mutual respect, especially after they discuss their shared goal of surpassing Rin and Nagi. Reo’s hidden ability to use Metavision becomes a turning point in their relationship, and while they remain rivals, they share a more amicable bond.

Jinpachi Ego

Ego’s philosophy initially intrigues Isagi, and he becomes one of the first players to embrace Ego’s vision for football. Throughout Isagi’s journey, Ego commends his growth, especially his ability to shadow Rin Itoshi. When Blue Lock faces challenges, Isagi becomes more focused on winning, impressing Ego with his passion and commitment.

Anri Teieri

Anri and Isagi first meet when she distributes the Blue Lock uniforms. Though she did not initially choose him, Anri later witnesses his growth, recognizing his potential as a player. Unlike the other Blue Lock participants, Isagi’s path to the program was personally chosen by Ego.

Ryosuke Kira

Kira is Isagi’s first friend in Blue Lock, recognizing him from their previous match in the Saitama Prefecture Finals. They share a brief bond before Kira is eliminated, angry at Isagi for being the one to take him out. Despite their initial camaraderie, Kira’s departure from Blue Lock ends their friendship on a sour note.

Itoshi Rin

Rin and Isagi’s rivalry begins when Rin effortlessly defeats Isagi in the Second Selection. Isagi vows to surpass Rin, but Rin remains indifferent. They meet again in the Fourth Stage, where Rin admits his respect for Isagi’s persistence. Their rivalry continues, with Isagi seeing Rin as a source of motivation, while Rin considers Isagi a non-issue. However, by the Neo Egoist League, Isagi grows closer to Rin’s level of skill, vowing to catch up and surpass him one day.

Noel Noa

Noel is Isagi’s idol, and his excitement to be coached by Noa in the Neo Egoist League drives him to join Bastard München. However, Isagi’s admiration wanes when he realizes Noa has been using him to help his rival, Michael Kaiser, develop his ego. This revelation fuels Isagi’s determination to defeat both Noa and Kaiser, marking the end of his idolization and the beginning of a more intense rivalry.

Michael Kaiser

Kaiser’s arrogant demeanor immediately clashes with Isagi’s competitive spirit. Despite their animosity, Isagi respects Kaiser’s abilities and views him as a significant obstacle in the Neo Egoist League. The rivalry between them continues to evolve, with Isagi striving to surpass Kaiser and prove himself as the best striker.