In Episode 31, the battle between Blue Lock XI and Japan's U-20 team intensifies. Bachira launches an attack but is intercepted by Oliver Aiku, the U-20 team's captain and a defender with impressive awareness and reflexes. Isagi recognizes Aiku's exceptional defensive skills and knows they must overcome him to win.

Searching for new strategies, Isagi shifts the attack to the right wing, where Otoya is tightly marked by Darai, who counters his every move. They switch to the left wing, bringing Yukimiya into play, but he is also stopped by Neru, a speedy defender. Nagi tries to take control but is shut down by Niou's aggressive pressing.

The U-20's "Iron Four Defense" proves nearly impenetrable and enables a swift counterattack. Itoshi Sae, the U-20 team's star midfielder, takes possession of the ball. Despite Chigiri's attempts to defend, Sae delivers a precise, long cross-field pass. The U-20 team pushes forward, but Gagamaru makes a crucial save. However, Sae secures the rebound and scores from a difficult angle, making it 1-0 for the U-20 team.

The crowd erupts in cheers for Sae, highlighting Blue Lock's underdog status. Rin urges Isagi to stay focused and promises to turn the tide. The team adjusts their tactics, and Rin and Isagi increase their coordination and passing speed to disrupt the U-20 defenders. Bachira supports them by distracting defenders and creating openings.

Amid the chaos, Nagi receives the ball, executes an impressive technique, and scores the equalizer—1-1. The Blue Lock team celebrates this breakthrough after penetrating the U-20 defense. The episode ends with Reo contemplating how to reconnect with Nagi. Chigiri advises him to seize the opportunity to express his feelings, as nothing is certain in Blue Lock, and every chance must be taken.