Popp is one of the central characters of the series and largely functions as its deuteragonist. He is a fifteen-year-old boy from the village of Lankarks, the only son of the weapons merchant Junk and his wife Steenie. After the legendary hero Avan passed through his village, Popp became deeply inspired by his strength and ran away from home to become his apprentice. He later travels alongside Avan to Dermline Island, where he meets Dai and becomes his senior fellow disciple.

At the beginning of the story, Popp is cowardly, lazy, and prone to boasting. He avoids difficult training, loses his nerve against strong opponents, and has a habit of making excuses or trying to flee when danger appears. He also has a cheeky and lecherous side, frequently cracking jokes and complaining, which makes him a source of comic relief. Over time, however, he grows considerably. His friendship with Dai and the influence of the people he meets gradually push him to find real courage. He develops into a dependable fighter who is willing to put his own life at risk to protect his companions, and he becomes a calm, clever tactician known for provoking enemies into lowering their guard. The story presents him as the most ordinary member of the main group, and his journey illustrates how a plain individual with no special bloodline can rise through determination and willpower.

Popp's motivations evolve from self-interest to loyalty. Early on, he is mainly concerned with his own safety and comfort, but he gradually becomes driven by a desire to protect his friends and to prove his worth as a magician. His love for Maam is a particularly strong source of motivation, inspiring him to be braver and strive for greater strength. He also struggles with deep feelings of inferiority, since his companions all come from remarkable backgrounds: Dai is a Dragon Knight, Leona is a princess, Maam is the child of famous heroes, and Hyunckel is a highly trained warrior. Popp is simply the son of a small village merchant, and this contrast weighs on him until he awakens to his own unique strength.

Within the story, Popp serves as Dai's closest companion and the principal magic user of Avan's disciples. His role grows beyond casting spells; he becomes Dai's strongest emotional support and the group's strategic brain. Both allies and enemies come to acknowledge his abilities, and the forces of the Demon King eventually regard him as one of the most dangerous members of the hero party, with some even stating that he is the most feared of Avan's disciples.

His relationships are central to his growth. Avan is his mentor, who takes him in despite his weak disposition and hopes that time with Dai will change him for the better. Dai and Popp form an unbreakable partnership, with each willing to do anything for the other. Maam, his love interest, gives him a personal reason to become stronger, even though their relationship begins with conflict and disappointment. During the journey, Popp becomes a student of Matoriv, a legendary great mage and former companion of Avan, who subjects him to grueling training and ultimately teaches him the supreme annihilation spell Medoroa. Popp's relationship with Hyunckel is also significant, as he initially sees him as a rival for Maam's heart but eventually respects him as a fellow disciple of Avan.

Popp's development is marked by several major turning points. He first demonstrates genuine courage in a confrontation with the enemy general Crocodine, willingly facing an opponent far stronger than himself for the sake of a friend. During the conflict with Baran, he goes even further. When Dai loses his memory and is turned against his comrades, Popp chooses to sacrifice himself by using the self-destructive spell Megante, giving his life to shock Dai's memories back. His love for his friend moves even Baran, and through a combination of dragon blood, the divine tears stored within the creature Gome, and his own powerful will, Popp is brought back from the dead. His most important moment of personal growth comes during the preparations for the spell Minakator. When he fails to make the Mark of Avan shine, he falls into despair, convinced that he alone has no special power. The young woman Merle, who secretly loves him, is gravely wounded while shielding him, and her dying request is to know whom he loves. His confession of his feelings for Maam awakens his soul force of courage, causing his mark to shine green and unlocking the powers of a sage. He is then able to instantly heal Merle with recovery magic of an extraordinary level. From that point onward, he stops comparing himself with others and rapidly matures into a truly formidable magician.

In terms of abilities, Popp specializes in elemental attack spells. He is particularly skilled with fire-type spells such as Mera, Merami, and Merazoma, and he also uses ice-type spells. His arsenal later expands to include the gravity pressure attack Betan, and after completing his training with Matoriv, he masters Medoroa, one of the most powerful spells in the entire series, which combines fire and ice into a devastating destructive force. He also receives a staff from the legendary smith Lon Berk, a weapon that can change shape and that rivals the power of the Demon King Vearn's own staff. In the final battles, Popp displays extraordinary magical control, including casting two spells at the same time, deflecting and reflecting enemy magic using the mirror entrusted to him by the warrior Sigma, and even tearing apart the Demon King's overwhelming Kaiser Phoenix attack by concentrating his magical energy. By the end of the story, he has become one of the strongest human mages in the world, though he prefers to call himself a great mage rather than a sage.