Jeremiah Gottwald begins his journey in the story as an elite Britannian military officer who holds the rank of Margrave and is a leading member of the Pureblood faction, a group that advocates for the supremacy of pure-blooded Britannians over the conquered peoples known as Numbers. His background is deeply rooted in a significant personal failure; as a young soldier, he was part of the guard at the Aries Palace when Empress Marianne was assassinated. This event, which he considers the first great failure of his life, haunts him and becomes the primary motivation for his actions. He later transfers to the Area formerly known as Japan, believing it to be the land where the empress's children, Lelouch and Nunnally, met their end, and hopes to redeem himself through service.

In his initial role within the narrative, Jeremiah is an antagonist driven by a strong sense of duty and a desire for personal redemption. He attempts to use the Honorary Britannian Suzaku Kururugi as a scapegoat for the murder of Prince Clovis, a plan that backfires spectacularly when the masked rebel Zero appears. During the public execution, Zero destroys Jeremiah's reputation by calling him "Orange," a seemingly nonsensical codeword that Lelouch uses in conjunction with his Geass power to force Jeremiah into helping the terrorists escape. This "Orange Incident" leads to his social and professional ruin; he is demoted, mocked by his peers with the nickname, and becomes obsessed with capturing Zero to restore his honor.

Jeremiah's rash and impulsive nature leads to his near-death during the Battle of Narita. After being gravely wounded, his body is recovered by a team of scientists working for Prince Schneizel. They subject him to extensive cybernetic experimentation, transforming him into a powerful cyborg. His mind is tampered with, and he becomes unstable, fixated on destroying Zero. He escapes and pilots a massive weapon called the Siegfried, only to be seemingly destroyed in combat. He survives, however, and resurfaces as an ally of V.V., equipped with his most notable ability: the Geass Canceler. This power, housed in his cybernetic left eye, allows him to nullify the effects of any other Geass within a certain range, restoring memories that have been altered or erased. His other implants grant him enhanced combat abilities, retractable blades, bulletproof armor, and advanced sensory perception.

The turning point for Jeremiah comes when he confronts Lelouch directly and learns the truth of his identity and motives. Lelouch reveals that he is the son of Empress Marianne and that he became Zero to avenge her murder. Upon hearing this, Jeremiah regains his sanity and experiences a total shift in allegiance. His loyalty, which had always been rooted in his service to the late empress, is now transferred to her son. He swears absolute fealty to Lelouch and reclaims the insulting moniker "Orange" as a badge of honor, renaming it the "name of his loyalty." From this point, he transforms from a persistent enemy into one of Lelouch's most trusted and formidable retainers.

His key relationships are defined by this evolving sense of loyalty. He maintains a complex connection with Suzaku Kururugi; despite their violent encounters, he acknowledges a peculiar bond with the man who once rescued him from an assassination attempt by his own allies. His relationship with Lelouch becomes the central pillar of his existence, as he dedicates himself to serving Lelouch's goals and protecting Nunnally, the sister of his new liege. He also has a significant connection to Villetta Nu, a subordinate who remained loyal to him during his disgrace. In the final battles, he uses his Geass Canceler to free the Knight of Rounds, Anya Alstreim, from a Geass affecting her memories, demonstrating the practical application of his unique power in service to Lelouch's cause.

Throughout the second season, Jeremiah's development is a complete arc from disgraced, fanatical enemy to a paragon of chivalrous devotion. He abandons his former xenophobic ideals to serve a man who fights against the empire Jeremiah once served. At the conclusion of the major conflicts, he shows his understanding of and cooperation with Lelouch's ultimate plan, the Zero Requiem, by allowing Suzaku, disguised as Zero, to pass through his lines. In the series' epilogue, Jeremiah is seen peacefully cultivating an orange farm in the countryside, alongside Anya Alstreim, having found a final, quiet redemption far from the fields of battle. His notable abilities include his elite piloting skills, his cybernetically enhanced body, and his unique and invaluable Geass Canceler, which makes him a perfect counter to other Geass users and a key instrument in restoring the memories of those manipulated by the power.