Cain Barzad is an elderly former Holy Knight from the now-destroyed Kingdom of Danafor. He is a man of short stature, standing at 155 centimeters, with gray hair, a long mustache and beard, and eyes that are almost always depicted as closed or squinting. During his active years as a knight, he was never seen without a full set of armor that completely concealed his face. This habit meant that his former comrade, Meliodas, did not recognize Cain’s face when they met again years later. In the present, Cain typically dresses in a cloak over a shirt bearing the crest of Danafor, a symbol of his continued loyalty to his lost homeland.

In personality, Cain initially appears as a jovial, friendly, and somewhat disheveled drunkard who greets people with a casual "Yo". He exhibits a youthful enthusiasm and a passion for drinking. However, this carefree exterior masks a deep well of survivor’s guilt, sorrow, and a fierce sense of honor. He is deeply marked by the destruction of Danafor, being the only known survivor of the tragedy because he was away on a mission in another country at the time. This loss drives a serious and passionate side to his character, making him fiercely protective of the ideals of his fallen kingdom and deeply suspicious of anyone he believes may have betrayed it.

Cain's primary motivation throughout his appearance in the story is to uncover the truth about what destroyed Danafor. Having heard rumors that Meliodas, the captain of the Seven Deadly Sins and a fellow former knight of Danafor, was responsible for the catastrophe, Cain seeks him out. He enters the Vaizel Fighting Festival, a tournament he guides the Seven Deadly Sins to, with the specific intention of confronting Meliodas. He seeks not only answers but also a form of retribution, believing that Meliodas betrayed everything he had sworn to protect, including the kingdom, its people, and the person most important to him.

In the narrative, Cain serves as a living link to Meliodas's mysterious past in Danafor. His role is primarily during the Vaizel Festival arc, where he acts as a guide to the Sins and later becomes a contestant. He first demonstrates his skill by quickly knocking the Sin of Sloth, King, out of the arena. His most significant moment comes when he faces Meliodas in a match. At first, Cain mistakes Meliodas for his own son, but upon learning his true identity, he unleashes his pent-up grief and anger, attacking the man he holds responsible for his kingdom's fall. The confrontation does not result in a final victory for either; instead, it serves as a catalyst for reconciliation. When Meliodas assures him of his innocence regarding Danafor's destruction, Cain is visibly moved and weeps with relief, rekindling their old friendship.

Cain’s most important relationship is with Meliodas. In the past, they were comrades in the Holy Knights of Danafor. Cain had a deep respect for Meliodas, even if he sometimes disagreed with his decisions, such as sparing the life of a woman named Liz. Over time, Cain grew to accept and care for Liz, and he was deeply saddened by her death. This history makes the perceived betrayal by Meliodas all the more painful. After their reconciliation, their bond is restored, demonstrating Cain’s capacity for forgiveness. He also shares a significant, albeit brief, relationship with Elizabeth Liones. Upon first seeing her, he is struck by her resemblance to Liz and initially mistakes her for a returned spirit. He shows trust and kindness toward her, entrusting her with a precious small sword that once belonged to Liz, asking her to deliver it to Meliodas during a battle. Cain also demonstrates a friendly rapport with the other characters, such as the former mountain bandit Taizoo.

While Cain does not undergo a dramatic personal transformation, his character arc is one of closure. He develops from a man consumed by survivor’s guilt and a thirst for blame into a figure who can finally lay his past to rest. The resolution with Meliodas allows him to move forward, still loyal to the memory of Danafor but freed from the anger that had defined his quest for revenge.

Regarding his abilities, despite his appearance as an old man with a bad back and a drinking problem, Cain Barzad is a remarkably capable fighter. He possesses significant physical strength and speed, capable of moving in an instant and punching an opponent out of a large arena ring. His unique magical power is called Blaze. This ability allows him to create, control, and release powerful, searing flames at will. During his time as a Holy Knight, this mastery over fire earned him the formidable epithet of "The Flame Barzad", a title by which he was more widely known than his real name.