Judeau is first seen when he sees Guts receive a punch to his shoulder wound from Casca, telling him that was because Casca had to sleep with him to keep him warm for the two nights he was asleep. After Guts' first battle with the Hawks, Judeau goes to see him with Rickert and Pippin and orders Pippin to carry Guts down to the campsite to party with the other Hawks, stating that it was not only a party for victory but also Guts' welcoming party. He later meets Guts in the morning and states that he might find his reason for living in joining the Hawks, and provides some insight into Griffith's character as something that can't be nailed down. During the three-year gap between Guts' membership and the Hawks' integration, Judeau teaches Guts to throw knives and actually later adapts to using the knives that Guts uses. Judeau survives on the battlefield with his twin swords and frequently looks out for Casca, trying to assist her in defeating Adon Coborlwitz after she proves to have some difficulty doing so. When Casca is about to be raped by one of Adon's soldiers sent to chase her, Judeau leads a division of the Hawks and kills off the chasing soldiers, stating that Casca is the Hawks' only flower and that he won't let anyone defile her. After the battle, Judeau gives the elf dust to Casca to heal Guts' wounds, realizing how much Guts wanted to battle.
After the battle of Doldrey, Judeau is later seen talking to Guts about leaving the Hawks, Though he provides several reasonable answers to Guts' decision, among them to take Casca with him and suggesting that Casca loves him, all are disregarded. He is among those who witness Griffith's defeat and Guts' leave and the survivors after the Hawks are decimated by Midland's armies.
During the year the Hawks are on the run, Judeau attempts to take care of Casca while the latter commands the Hawks and even tries to take on some of her responsibilities. He is among the Hawks to welcome Guts' return and one of the few to head to the Tower of Rebirth to rescue Griffith. Guts compliments him for being "brilliant" for using sparks to temporarily find the location of the attacking Bākiraka.
When the Hawks are decimated following Griffith's arrest and subsequent rescue, he briefly considers forming a band of thieves with some of the other survivors as a means of keeping the now-crippled Griffith safe; he suggests that such a life would not suit Casca and asks Guts to take her away. Unfortunately, Judeau is Branded on the palm of his left hand and sacrificed along with the rest of the Hawks. He dies attempting to protect Casca from the Apostles' bloody rampage and even goes as far as to throw himself on top of her to shield her from attack by an Apostle with whiplike tentacles that wound him horribly after his horse is eaten alive, putting out the Apostle's eye with his last throwing knife so that Casca can finish it off. In his final moments, knowing that his end is drawing near, he attempts to tell Casca that he loves her, but does not gain the courage to do so and dies in her arms.