Kakeru Aizawa is the younger brother of Suguru Aizawa, a soccer prodigy who represents Japan in the under-fifteen national team. Kakeru plays as a forward, though his journey to the position is marked by significant psychological hurdles. As a sixth grader, he severely injured a friend and teammate, Hibino, by kicking the ball powerfully with his left foot. The trauma from this incident caused Kakeru to become deeply wary of using his left leg, a fear that seriously hindered his ability to score goals and severely damaged his confidence. This psychological block was so profound that he seemed unable to score at all, leading him to gradually step back from playing competitively and instead take on the role of assistant manager for his school's football club, a decision that frustrated his talented older brother.

In terms of personality, Kakeru is generally a positive and kind individual, but his defining characteristic is a marked lack of confidence. This insecurity is the root cause of his inability to use his left leg and his reluctance to return to the pitch as a player. When serving as the team's manager, he carried out demanding and sometimes menial tasks with a smile, even enduring the humiliation of being called the inferior sibling by his peers. Beneath this exterior, however, he maintained his passion for the sport by secretly practicing soccer every night in a local park. Despite his fears and self-doubt, Kakeru possesses a keen sense of the ball and a natural ability to create scoring opportunities even against the tightest defenses, hinting at the talented striker he was meant to be.

Kakeru's primary motivation becomes intrinsically linked to his brother after a tragic accident. Shortly after a sincere conversation in which Suguru told Kakeru that a king cannot win alone and needed a courageous knight to lead the team to victory, the two brothers were hit by a truck. Suguru suffered fatal head injuries, while Kakeru's heart was irreparably damaged. To save Kakeru's life, Suguru's heart was transplanted into his younger brother. Upon recovering and learning that his brother's final wish, or last pass as he came to see it, was for them to win the World Cup together, Kakeru decides to return to football with the unwavering goal of achieving that dream.

The story follows Kakeru's journey as he re-enters the world of competitive soccer. His role is that of a protagonist overcoming immense personal tragedy and psychological barriers. He begins at Kamakura Middle School, where he earned the embarrassing nickname Mr. No Goal, but he eventually transfers to Enoshima High School. He enrolls there specifically to receive passes from a player named Araki, whom his brother had praised for his exceptional skills. At Enoshima, Kakeru finds himself in a complicated situation with a split soccer club, joining a hobby group known as the Football Club with the hope of revitalizing it and leading his team to the national championships.

Key relationships heavily influence Kakeru's development. His bond with his late brother Suguru is the emotional core of the series. Suguru recognized Kakeru's natural talents and desperately wanted him to fulfill his potential, a desire that posthumously drives Kakeru forward. He also shares a significant relationship with Nana Mishima, a childhood friend and old crush who is a talented player known as the Little Witch. After returning from the United States, Nana becomes the team's manager and is revealed to be the mysterious masked figure who challenged Kakeru to nightly practice matches at Suguru's request, helping him rediscover his love for the game. She is instrumental in his recovery and continued growth as a player.

Kakeru undergoes substantial development throughout the series. Initially paralyzed by fear and lacking confidence, he gradually transforms into a determined and courageous striker. After the heart transplant, he seemingly inherits some of Suguru's skills and temperament, and he overcomes his psychological block against using his left leg. He relentlessly trains to improve, working to fix weaknesses such as a tendency to look at the ball before feinting, which made his intentions too obvious to opponents. While he still has moments of nervousness when top players pay attention to him, his resolve on the field becomes unshakable. His journey is one of growing from a frightened boy who ran away from the game into the knight his brother always believed he could be.

Regarding notable abilities, Kakeru's primary asset is his exceptional instinct and spatial awareness. He has a rare knack for creating goal-scoring chances from seemingly impossible situations. After the accident and his recovery, he regains full use of his left leg, which had been his Achilles' heel. He also sometimes exhibits high-level dribbling skills that mimic those of his late brother. His physical build is small and somewhat short, which belies his high endurance and strength on the pitch. As a central forward, his game is not based on raw power but on intelligent positioning, sudden bursts of speed, and an almost preternatural ability to be in the right place at the right time to finish an attack.