Cornelius/Story

Before Rozemyne moves into Karstedt’s estate, Cornelius is briefed on her original fake backstory, as the daughter of Rozemary. He is upset to be assigned as her guard knight against his wishes, and he worries that accepting Rozemary’s daughter will reignite the family conflict. When he meets her, however, he takes a liking to her and accepts her as his sister.

In an attempt to bond with her, Cornelius later takes Rozemyne to the estate’s book room. However, she faints on the way there after walking too quickly. Ferdinand explains that he intended the harsh lesson to make Cornelius aware of how frail his sister really is, without actually putting her health at risk. Cornelius suggests they do something similar for Wilfried.

Cornelius is present at Rozemyne’s noble baptism, and he is visibly worried that it will go well. Lured by the prospect of new foods, he later forces his way into serving as Rozemyne’s guard during Sylvester’s visit to the Italian Restaurant, despite being underage and technically not allowed outside of the Noble’s District. When they unexpectedly travel to Hasse after the meal, Cornelius carries Gustav on his highbeast.

Lamprecht approaches Cornelius in the winter playroom to ask whether he has vetted Rozemyne’s future retainers yet. During the conversation, Cornelius admits that while he originally intended to serve Rozemyne only until she turned ten and went to the Royal Academy, he is considering serving her after that as well.

When Angelica is required to take supplementary lessons at the Royal Academy, Cornelius is taken aback by how little she remembers from her schoolwork. Rozemyne reflects that, while Cornelius relies on his mana too much and struggles in his written classes, he still maintains acceptable grades. When Rozemyne offers a reward for helping on the “Raise Angelica’s Grades Squadron,” Cornelius asks for new sweets or recipes.

Cornelius works hard as a member of the “Raise Angelica’s Grades Squadron” and studies ahead using Eckhart’s study materials from his student days. He learns tactics from Damuel using gewinnen and takes the brunt of the responsibility for tutoring Angelica. As his reward, Rozemyne gives him a recipe for Mont Blanc made with tanieh cream, his favorite kind of sweet.

When Angelica’s manablade, Stenluke, gains sentience, Cornelius helps create a fourth-year study plan for her, taking the sword’s intelligence into consideration.

When Rozemyne begins teaching her mana compression method to the archducal family and their retainers, Cornelius is among her students. He proudly resolves to increase his mana capacity even more than his older brothers.

Cornelius serves as Rozemyne’s guard knight during Charlotte’s baptism. When Charlotte is later kidnapped, he follows Rozemyne who rushes off in pursuit. Thanks to his quick reflexes, he is able to save Angelica and Charlotte when they are thrown from the assailant’s highbeast. However, while he is distracted, Rozemyne is captured in an enchanted net and dragged to the ground. He searches for her in the forest, but she is poisoned and carried away on horseback.

Rozemyne is later rescued by Bonifatius and Ferdinand, and Cornelius catches up with them and apologizes to his unresponsive sister. He gives Ferdinand her highbeast feystone for safekeeping, and then goes with Bonifatius to attempt to capture the remaining assailants. They apprehend Viscount Joisontak, and Cornelius reports to Aub Ehrenfest to prepare for interrogation. Afterward, he begins his grueling training under Bonifatius with Angelica, Damuel, Brigitte, and the other knights of the archducal family.

By the time Rozemyne awakens, Cornelius has grown much stronger under Bonifatius’s training. Due to his status as an archnoble, he will serve as her head knight in the Royal Academy and at the castle, while Damuel remains the leader of the guard knights at the temple.

During the winter debut, Cornelius warns Rozemyne that their half-brother Nikolaus, the son of Karstedt’s second wife Trudeliede, will be among the children present. He reminds her not to show any favoritism to him, despite technically being family.

Cornelius leaves for the Royal Academy the day before Rozemyne and is present to greet her when she arrives. He provides her a list of retainers which she uses to make her final selection. When Angelica is forbidden to use Stenluke in classes, Cornelius — who is now an honor student — devotes himself to tutoring her to so she can pass her classes and graduate.

When Rozemyne collapses in the Farthest Hall while obtaining the Divine Will for her schtappe, Cornelius is visibly distraught. He is very relieved when he hears news of her recovery.

During the treasure-stealing ditter match between Dunkelfelger and Ehrenfest over the ownership of Schwartz and Weiss, Cornelius competes as a member of the Ehrenfest team. He shows strong leadership skills, and his remarkable mana capacity allows him to deliver the finishing blow to the opposing team’s feybeast.

Cornelius later spends a lot of time researching battle tactics and feybeasts in the library with Leonore. Observing them studying in the same carrel, Rozemyne muses that they look like a couple on a date.

When Traugott resigns from Rozemyne's service, Cornelius is relieved. Although they were cousins, he had to put up with Traugott’s antagonism and one-sided rivalry from an early age.

While staying in the Ehrenfest dormitory together, Cornelius and Rozemyne treat each other more familiarly as siblings because there are fewer adults around. The other retainers often remark on how close they are.

Cornelius accompanies Rozemyne when she returns to Ehrenfest for the Dedication Ritual. However, she leaves for the temple almost immediately. Since Cornelius is still underage, he is not allowed to accompany her. Instead, he uses the time to write reports, learn from his father, and sit in on meetings of the Knight's Order.

As Ehrenfest prepares for the Interduchy Tournament at the Royal Academy, Cornelius and Angelica are in charge of the apprentice knight ditter team, while Leonore acts as a tactical advisor. He later reports that their performance in the match was “not as good as one would expect for our rank,” but still much better than previous mock battles.

He is once again chosen as an honor student at the end of the year. When Rozemyne returns to Ehrenfest, Cornelius’s quick reflexes save her from being thrown into the ceiling by Bonifatius.

Spoiler from Part 4 Volume 6 Cornelius already has a girl firmly in mind who he will ask to escort at their mutual graduation ceremony. Because he is worried about Rozemyne leaking her identity to Elvira who would very likely use this as material for a new romance novel, Cornelius keeps it under wraps for the time being and intends to ask approach the girl during Rozemyne's scheduled absence from the academy for the Dedication Ritual.

Following Rozemyne's schtappe transformation class Hartmut learns that Rozemyne had turned her schtappe into a new kind of weapon and accidentally shredded her bed's canopy with it and is eager to see this new weapon. Albeit reluctantly Rozemyne eventually caves and shows off her water-gun, though more likely due to Leonore potentially being able to derive some practical use rather than just to satisfy Hartmut curiosity.

At Leonore's suggestion the trio, accompanied by Cornelius and Judithe, head to Ehrenfest's gathering spot where Rozemyne tests her new gun against a feybeast. There she fires her gun and turns the water that comes out of the guns muzzle into an arrow that splits apart into multiple projectiles, like she had seen Ferdinand do in the past, badly wounding the animal. Cornelius quickly rushes in to finish it off after which the group retreats outside the barrier. Rozemyne is disappointed she wasn't able to slay the beast in a single attack, but Cornelius informs her that it was a rather strong one and that he is impressed with how much damage she was able to inflict on it.

Spoiler from Part 4 Volume 8 In his final year at the Royal Academy, Cornelius manages to be among the thirteen Ehrenfest's students who are able to attain honor student status.

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