Jean Colbert is a professor at the Tristain Academy of Magic, where he teaches history and is deeply interested in science and ancient artifacts. He is a Square-class mage whose primary elemental affinity is fire, making him one of the most skilled and powerful magic users in the setting. Prior to his academic life, he served as a military captain leading mage troops into battle, a period during which he was given the feared nickname the Flame Snake.

His personality is defined by a strong pacifistic attitude, a direct result of guilt over his violent past. He harbors a deep remorse for his actions as a soldier, most notably for leading an attack that burned down a village, including the home of a young girl named Agnès, under the false pretense that the village was afflicted by a plague. Upon discovering the truth that the village was innocent, he rescued the child and has since dedicated himself to a philosophy of peace, rejecting his former life of violence. This guilt is his primary motivation, driving him to protect others and to seek knowledge that might lead to a better world. He expresses envy upon learning from the protagonist Saito that his world is not constantly ravaged by war.

In his role at the academy, Colbert serves as a mentor and a source of knowledge. He is subordinate to the headmaster, Old Osmond, and is a trusted teacher to students including Louise Françoise Le Blanc de La Vallière, Kirche Augusta Frederica von Anhalt Zerbst, Tabitha, Guiche de Gramont, and Montmorency. His key relationships are often tied to his past. He has a complex dynamic with Agnès, who eventually learns he was responsible for destroying her homeland. In an effort to protect her from the truth and allow her to move past her quest for vengeance, he stages his own death with the help of the student Tabitha. While this leads others to believe he is dead, he survives in secret and continues to aid his allies. He also forms a significant bond with Saito, the familiar summoned from Japan. Fascinated by the advanced technology from Saito’s world, Colbert dedicates himself to studying and replicating it. His successful attempt to create gasoline to fuel an airplane is a notable achievement from this research. He maintains a cordial relationship with Kirche, who is the one to reveal his given name, Jean, and is also noted as his love interest.

Throughout the story, Colbert undergoes significant development from a haunted former soldier to a proactive scholar of peace. While he initially hides from his past as the Flame Snake, he eventually confronts it to protect his students and find a form of redemption. His abilities are noteworthy; beyond his high rank as a Square-class fire mage, which he rarely uses in combat due to his pacifism, his greatest talent lies in his intellectual curiosity. He is a pioneering figure in his world for bridging the gap between magic and technology, using his knowledge to reverse-engineer devices and fuels from another dimension.