Cornelia Arnim (pronounced /kɔɹˈniliə ˈɑɹnɪm/]; Japanese: コルネリア=アルニム Cornelia Arnim) is a non-playable character appearing Fire Emblem: Three Houses. She is a court mage in service of the Holy Kingdom of Faerghus.

Cornelia Arnim is a scholar from the Adrestian Empire who was an old acquaintance of Anselma von Arundel. In Imperial Year 1165, she left the Empire to travel to the Holy Kingdom of Faerghus, where she cured a plague that was devastating the Kingdom's populace. For her deeds, King Lambert appointed the Adrestian scholar the position of Court mage. In 1168, Cornelia found a young Hapi who had run away from her village, and provided her shelter and food while also subjecting Hapi to many painful experiments. During the Insurrection of the Seven in 1171, Cornelia helped Anselma escape to the Kingdom in secret and provided her shelter as well. When Volkhard von Arundel and Edelgard, Anselma's brother and daughter respectively, arrived to Faerghus concealed from the public, Cornelia informed Anselma of the news while claiming Lambert was deliberately keeping her away from Edelgard. In 1176, Cornelia freed Hapi and eventually persuaded Anselma into taking part on the Tragedy of Duscur, promising her she would be able to see her daughter again who had left the Kingdom territories along with her uncle 2 years prior.

In 1181 of the Silver Snow, Azure Moon and Verdant Wind routes, Cornelia murders Rufus, the Kingdom's regent, frames Dimitri for the deed and publicly announces his execution, when in reality the crown prince had managed to escape from his predicament thanks to his vassal's support. With him gone, Cornelia pledges loyalty to the Empire and turns the Kingdom territories loyal to her into the Faerghus Dukedom, as she supports Adrestia's goal of unifying Fódlan. On Azure Moon, Dimitri and Kingdom Army eventually make their way towards Fhirdiad, which causes the oppressed citizens in Cornelia's rule to revolt against her. Unable to divert forces to suppress the rebellion, Cornelia grumbles about how he and Edelgard should have just killed each other and deploys Titanus as well some Viskam to face the enemy. Once Cornelia is defeated and mortally wounded, Dimitri asks her if she has any last words, giving her the opportunity to reveal Anselma's -Dimitri's stepmother- involvement with the tragedy before drawing her last breath. Meanwhile, On the Silver Snow and Verdant Wind routes, it is mentioned Cornelia suddenly vanished from the Faerghus Dukedom right after Edelgard's death,leaving her whereabouts after the war unknown.

On the Crimson Flower route, Cornelia is unable to pull her scheme from other routes and, along with Rodrigue, Gwendal and non-recruited Felix and Ingrid, guards Fort Arianrhod during the war. When Cornelia get the news Edelgard and the adrestian army are about to besiege them, she's at first shocked as she had not been given any prior intel of the Empire's sudden change of plans, but later calmly accepts this situation and chooses to prepare for the upcoming fight by unleashing her Titanus on the upcoming enemy army, secretly hoping some of the Kingdom forces would end up killed in the ensuing chaos as well. Once she is finally defeated, Cornelia takes her death with grace and simply laughs as she murmurs everything had gone exactly as planned, calling it a "delightful dance". After her demise, Lord Arundel reveals to the Adrestian Emperor that Cornelia had served him and was planning to sabotage Faerghus before her attempts were cut short due to Edelgard's sudden change of plans.

It is mentioned in-game Cornelia had a sudden shift in personality sometime after being granted her new position in the Kingdom, which is consistent with other characters killed and replaced by Agarthan infiltrators. Taking into account her access to those who slither in the dark's resources and her loyalty to Lord Arundel, it is implied she was murdered sometime after solving the Kingdom's epidemic sometime between Imperial Year 1165 and 1168, and that the woman the player has known as Cornelia is actually a high-ranking Agarthan impersonating her.

Community content is available under CC-BY-SA unless otherwise noted.