Itoshi Sae, a genius midfielder, returned to Japan disillusioned by the world stage but searching for a true striker. Shidou Ryusei, a violent, instinct-driven forward, lived only for the biological ecstasy of scoring. While Blue Lock found Shidou too volatile, Sae recognized his elite talent and chose him to lead the U-20 team's attack. Together, Sae’s flawless passes and Shidou's extreme athleticism created a destructive chemical reaction, forging a rare, mutual football respect.

Ryusei Shidou, the "Demon" of *Blue Lock*, is a hyper-violent, mercurial striker who views football through a primal, biological lens. To him, scoring goals is a form of genetic self-expression and survival. He rejects traditional teamwork, craving high-level "explosions" from elite players while dismissing average talent as "trash." His volatility led to constant clashes with rival Rin Itoshi, but his raw talent is undeniable. After famously eliminating Kunigami, Shidou was deemed too toxic for the Blue Lock Eleven. Instead, genius playmaker Sae Itoshi recruited him for the Japan U-20 team. Sae’s calculated passes perfectly unlocked Shidou’s chaotic nature, triggering a "Flow State" and a legendary acrobatic goal. He later joined France's Paris X Gen in the Neo-Egoist League. On the pitch, Shidou is the ultimate penalty-box predator. He possesses supernatural spatial awareness, instinctively sensing the goal’s position without looking. Combined with extreme physical flexibility, Shidou can score impossible, gravity-defying bicycle kicks and volleys from any body posture or angle.

Itoshi Sae began as a football prodigy, promising his younger brother Rin they would become the world's best striker duo. Leaving Japan to join Real Madrid's youth academy, Sae faced the brutal reality of global football. Disillusioned by the world's elite talent, he abandoned his dream of being a striker, reinventing himself as a genius midfielder. Returning to Japan with deep contempt for its football culture, he refused to play for the U-20 national team until he witnessed the Blue Lock project. Captivated by Shidou Ryusei’s volatile talent, Sae joined the U-20 side for the historic exhibition match. Despite their eventual defeat, the game reignited Sae's interest in Japanese football, shifting his focus to a new generation capable of producing a true striker.