Aelfric is a cardinal of the Church of Seiros tasked with overseeing the Abyss in Fire Emblem: Three Houses. Aelfric is described as kind and forgiving by those he oversees but he is also haunted by the death of Sitri Eisner. This led him to quietly plot to gather the descandant of the four apostles in order to use them as a desperate sacrifice to resurect Sitri with the fabled Chalice of Beginnings.
Aelfric serves as the main antagonist of the Cindered Shadows DLC of Three Houses. A dragon-like Aelfric also serves as the final boss of the DLC as he and Sitri's corpse are deformed and combined into the ferocious creature.
During his childhood, Aelfric was an orphan that ended up at Garreg Mach Monastery. It is there he met Sitri, whom he loved greatly. He also had great respect for Jeralt Eisner who then served the Knights of Seiros. Despite his love for Sitri, he was happy to see her marry Jeralt because he knew that she loved him. Sitri later died giving birth to Byleth Eisner. Aelfric was deeply affected by the news.
In 1170, Aelfric became a cardinal. He then was given his position as the overseer of the Abyss. Aelfric cared for its denizens and eventually made a plea to Rhea to have her allow the formation of an unofficial fourth house of the Officer Academy for the youths of the Abyss. This house was then dubbed the Ashen Wolves.
In 1175, while exploring Abyss, Aelfric stumbled upon Sitri's body, which was hidden there by Rhea who still visited her quite often according to herself. Despite having been dead for over 10 years, she was somehow still in perfect condition, likely due to the experiments Rhea had performed on her while she was alive.
If the DLC is completed, Aelfric has only a few mentions in White Clouds. It is mentioned that instead of enacting his plan to revive Sitri, he was expelled from the church due to a scandal just after the Rite of Rebirth.
Just after Flayn has been saved from the Death Knight, he will appear in front of Sitri's grave. He ask Byleth to bring him flowers to pay respect to his friend. He then tell Byleth to take care and that he doesn't have any regrets anymore before leaving.
Having heard of the Rite of Rising that was performed in the past by the legendary Seiros and the four apostles to bring back the dead, he began to plot Sitri's ressurection. He spent the next few years to gather the descendants of the Appostles; Yuri Leclerc, Constance von Nuvelle, Hapi, and Balthus von Albrecht; in the Abyss by finding ways to ostracize them from society while keeping his involvment secret to appear as their savior.
In 1180, Byleth alongside the three houses leaders; Edelgard von Hresvelg, Dimitri Alexandre Blaiddyd, and Claude von Riegan; alongside three other studens; Ashe Ubert, Hilda Valentine Goneril, and Linhardt von Hevring; find their way to the Abyss and fight the Ashen Wolves. After defeating them, they meet Aelfric for the first time and he tell Byleth more about both of his parents, which he obviously knew personally.
With Byleth's arrival, Aelfric starts to ennact his plan by capturing Yuri's mother and has him working for him in secret. The group manages to obtain the Chalice of Beginnings after believing that it was under threat. This plays in Aelfric's hands who then just has to play as Metodey's hostage and have Yuri betrays the group when they free him. By doing this, he manage to escape with the Chalice and the Ashen Wolves. He is soon after double crossed by Yuri who reveals that he had been working as an agent of Rhea all this time and that his mother had been rescued.
Aelfric immediatly begins the ritual regardless, which starts to magically drain the Ashen Wolves' blood. Byleth stops it before the Ashen Wolves bleed out but despite being incomplete, the ritual moves to its next stage. This cause the ritual to go haywire as a result. Aelfric and Sitri's corpse are absorbed by the Chalice who warp them into the Umbral Beast. The beast is eventually defeated by the students and Aelfric's body disappear with it.