Klaus is a tall man with a slender build and slanted light fuchsia eyes. He has a long, thin, and pointed nose with a large chin. His light blue colored hair is short and pushed to the sides and back while also having an angular fringe to his left-hand side. Additionally, he also wears a pair of gold, hooped earrings and dark glasses with rectangular frames. A diamond-like shape protrudes from the bridge of these glasses(seemingly fitted along his face). His glasses are usually pressed up against his face.
As a nobleman, Klaus dresses immaculately from top to bottom. He wears a double-breasted, long-sleeved shirt with a high collar(that reaches to approximately his adams apple) and gold-colored trimmings around the edges. The collar also has a chain connecting both ends of the collar as an ornament. The shirt itself is made of two different colors where it is light-colored at the side and dark-colored on the middle. The sleeves are mostly in light-colored fabric, except the wrist area where it has dark-colored fabric. The shirt extends below his waist and Klaus also wears a light-colored sash on top of it. Furthermore, Klaus also wears a casual light-colored pants and a pair of high boots to complement it. The dark-colored boots also have fur around the collar. Lastly, Klaus wear a long dark-colored robe on top of his outfit. The robe has enough length to cover his entire body.
As a member of the Golden Dawn squad, Klaus also wears the squad's signature robe. The robe is made of gold-colored fabric with faint gold patterns on the surface and only covers his torso. The hood also has a blue fur around the edges and a pair of blue rope coming out the left-hand side. The robes are attached to a gold button on the right-hand side where it keeps the robe together. Additionally, the squad's insignia is also positioned at the left-hand side of the robe.
Klaus is a prideful man who tends to judge people from their social standings regardless of their individual personalities or abilities. Additionally, he can also become very arrogant and starts insulting people of lower status than his without actually having a personal issue with them. This could stem from the fact that he is of noble birth and his membership in the best Magic Knights' squad of the Clover Kingdom. In contrast, Klaus can become a very loyal person towards people of higher status than him, such as his admiration towards William Vangeance.
Due to this inherit personality, Klaus became unable to easily acknowledge anyone, especially towards people whom are able to rise to his social standing regardless of their talents which lead them there. Furthermore, Klaus also finds shame over being assisted by people of lower social status than him in which can be seen from his constant denial of him being saved by a Black Bull squad member.
However, Klaus is still a man of reason as he is still able to judge and give his acknowledgement based on what he sees with his own eyes. This side of him is noted from his sudden approval of Asta and Yuno after witnessing their efforts and talents while completing the dungeon exploring mission. His acknowledgement also comes with a complete different kind of treatment as he is treating both Asta and Yuno as an equal squadmates of the Magic Knights. Klaus even goes as far as trying to defend Yuno against a fellow squad member whom has not acknowledged him just yet.
After being tasked to explore a newly emerged dungeon, Klaus then departs to the said dungeon along with his squadmates, Yuno and Mimosa Vermillion. After they manage to reach the inner-side of the dungeon and meet with another squad, the Black Bull, Klaus asks for Yuno's reasoning for saving the two members of the said squad from a trap. He then begins to have a series of argument with one of the Black Bull members, Asta. At the end, Klaus accepts a challenge from the other squad to see which one of them could reach the center of the dungeon first.
The Golden Dawn members then immediately depart with Yuno's magic after Mimosa locates their destination with her magic. Along the way, Klaus begins a discussion with his squadmates about the Black Bull but Yuno interjects him and warns him to stop underestimating Asta in which reminds Klaus that he has not acknowledges Yuno just yet.
Soon after, they arrive in front of the gate to the treasury at the center of the dungeon. Unfortunately, they are immediately confronted by a mage from the Diamond Kingdom whom manages to ambush Mimosa. The fight begins between Klaus and Yuno against the said mage, Mars. At first, the fight is on a stalemate with each sides is able to neutralize the others' attacks.
However, Klaus soon realizes that Mars' stamina and momentum do not seem to dissipate over time and quickly tells Yuno to abandon him and finish the mission of conquering the dungeon. During that time, Mars manages to find an opening to trap Klaus's left leg and about to give him a critical damage. Fortunately, Yuno decides to return and saves Klaus from the attack.
Klaus is then surprised by Yuno's full magical power but witnessing Yuno's inferiority against Mars even with the amount of magical power he possesses, renders him speechless. He then notices the crystals embedded on Mars' forehead in which triggers his memories of the rumors that the Diamond Kingdom had performed an experiment on their mages to forcefully enhance their magical power.
Upon seeing his own incapability to protect his squadmate, Mimosa, while being protected by a new member, Yuno, draws the prideful Klaus into the edge as he tries to attack Mars once again. However, Mars is able to easily overpower his attack by creating a crystal clone of himself which subsequently begins to attack Klaus instead while Mars continues his assaults on Yuno. Fortunately, Asta of the Black Bull squad manages to save Yuno while Luck Voltia is able to destroy the crystal clone. Seeing himself being saved by a member of the Black Bull squad quickly put shame on Klaus as he blames himself for it.
Klaus then, along with the Black Bull members, are put into the defensive side as Mars creates even more crystal clones of himself to attack them simultaneously. On top of everything that he has been witnessing, the fact that Asta is able to overpower Mars confuses him the most. Even after Noelle Silva reveals Asta's power, Klaus still believes that Asta took his unique power for granted. It is after seeing Asta's muscular build and his ambition of becoming the Magic Emperor that he stops vocally belittling him.
After Asta renders Mars unconscious, Klaus subsequently uses Restraining Magic to keep him in check before proceeding on entering the treasury. After a slight argument, all of them are able to enter with Asta forcefully cutting an entrance through the door. They are immediately being amazed by the amount of treasures that were stored within the dungeon. Each members immediately start to meddle with the various magic tools within the treasury, as soon as they enter, which frustrates Klaus as they might be very precious magical artifacts.
After a while, Luck suddenly warns them to step away from the door but Klaus was late to react as Mars storms into the treasury and traps him within a crystal structure. He then notices that Mars is using a fire magic spell in which surprises him as he knows that a mage can only use magic from a single element.
While being stuck within the crystal structure, Klaus is unable to use his grimoire as he can only witness as Mars is about to attack Mimosa and Noelle. When Asta comes to Mimosa and Noelle's side to help and releases a water-based attack, Klaus once again questions Asta's battle prowess as the latter is not supposed to possess any magical power.
The moment he sees Asta falls down due to Mars' attack, Klaus tries to rush his attempt of breaking Mars' binding with his magic but he did not manage to break free just in time. Fortunately, Yuno manages to defeat Mars through an unknown means and the crystals that were binding Klaus dissipate into thin air. When Klaus sees this phenomena, he immediately confirms that Mars has been completely defeated. Not long after, Klaus notices that the dungeon begins to shake as it is collapsing.
The moment the dungeon begins to collapse, Klaus immediately boards into a vessel that Yuno had created for them to escape. Klaus then tries to argue Asta's request to take Mars with them but Yuno decides to head towards Mars' location anyway. Unfortunately, they fail to pick up Mars and Klaus quickly asks Yuno to take them to the exit.
While Yuno is stirring the vessel according to Luck's guidance, Klaus uses his magic to destroy any falling debris around them alongside the latter. When they finally reach the exit, Klaus remains close to Asta as Mimosa is healing him. After a while, Asta is finally regaining his consciousness, Klaus quickly hugs him along with Yuno as he finally recognizes both of them as worthy members of the Clover Kingdom's Magic Knights.
A week after completing the mission, Klaus travels with his squadmates to the Noble region to give their report on the mission. Along the way, they encounter Asta and Noelle where they decide to head towards the designated venue together. Upon arrival, Klaus is shocked and quickly lowers his head when the Magic Emperor himself, Julius Novachrono, is greeting them. After a quick audience with Julius, Klaus and the rest of the dungeon exploring mission members are invited to attend a War Merits Conferment Ceremony in which awards several Magic Knights that have produced tremendous result over a period of time.
At the end of the ceremony, all of them yet again invited by Julius to attend the celebratory banquet in which the Emperor decided to leave them alone with the honorary Knights. After the Emperor had left, Klaus begins to sense various stares from his surrounding while complementing Asta for being able to withstand the scrutiny. Klaus tries to defend Yuno from Alecdora Sandler's, a fellow Golden Dawn members, insults but he receives similar critiques, instead. Klaus then can only watch in silence as Asta is confronting those Knights that have been humiliating them.
When someone enters the banquet hall and informs the Knights that the Royal Capital is under attack, Klaus joins his colleagues as they discuss a plan of counterattack. When Asta abruptly leaves the meeting, Klaus tries to stop him but he fails to convince the latter to stay. He then proceeds on going to the West District of the Royal Capital along with Hamon Caseus and Siren Tium. As they arrive at the location, they are immediately surrounded by an army of corpses, and the Knights proceed to decimate every last one of them in the vicinity.
After all of the corpses are defeated, a Spatial Magic spell activates and the Knights are transported a considerable distance away from the Royal Capital. Fortunately, Klaus is able to return to the Royal Capital in a short amount of time after combining his magical power with the rest of the stranded Knights. However, upon his arrival, he is unable to prevent the enemies from taking Asta away with them.
Noelle suggests for the Knights to pursue and rescue him, but Klaus disagrees with her as he explains their inability to trace the enemies' movements. Klaus then stays alongside his colleagues while Mimosa tries to heal Fuegoleon Vermillion. After the Vermillion brothers were sent to the medical ward, Klaus quickly shows his deep relief when Julius returns to the Royal Capital with Asta. The nobleman then stays with his colleagues as the Magic Emperor addresses them, in regards to the upcoming conflicts.
Later on, Klaus strolls around the Royal Capital with Mimosa and Yuno when they encounter the Black Bull members. The nobleman is stunned after one of his juniors suddenly launched an attack towards Asta and the other Black Bull mages. Klaus then begins to aware of Yuno's sudden growth in power after he saw the attack, but the nobleman decides to keep it to himself.
Months later, Klaus attends the Star Awards Festival and cheers for Yuno when he is recognized for the number of stars he collected. He later listens as Augustus Kira Clover XIII announces the Royal Knights Selection Exam.
A week later, Klaus admonishes Mimosa for causing problems with other Magic Knights at the exam and for being too relaxed. He then returns Asta's greeting, pointing out that he has been training. He is upset when he is placed on Team K with Luck and Puli Angel.
As the second match starts, Klaus tells Noelle to show some respect when she summarizes Kirsch Vermillion as gross, pointing out that Kirsch acts as the Coral Peacock's captain since Dorothy Unsworth is always asleep. After Team C wins, Klaus explains Kirsch's Magic Cherry Blossom Blizzard and points out that it requires royalty levels of magic.
As their first match begins, Klaus tries to reign in Luck's excitement and decides to take charge when he sees how similar his teammates are. During the match, Klaus successfully defends against the Azure Deer's attack but is then flanked, but Luck manages to save the crystal. Impressed by Luck's increased abilities, Klaus shows off his improvements by drilling through the Violet Orca's attack, and Luck challenges Klaus to a fight after the match. Klaus tells him to focus as they face their three opponents.
Coordinating their magic, Klaus launches Luck forward by raising a wall from the ground underneath the Black Bull's feet, while Puli boosts his speed further by creating a tailwind.  After Luck kicks Rob Vitesse into the crystal, destroying it and winning the match, Team K high-five each other.
During the eleventh match, Klaus is impressed with Langris Vaude's power and how quickly he cancelled his own reflected spell. As Asta collapses from exhaustion after defeating Langris, Magna catches him while Klaus and many other Knights take to the field in support of Asta.
During their second match, Team K plan to take out Rill Boismortier before he can exploit their weaknesses so they combine their magic to create Thunder Arrow, with Klaus providing a steel railgun. Despite the spell's speed and power, Rill redirects it back at Team K, shattering the crystal and winning the match.
Several days after the exam, Klaus and the others selected to be Royal Knights all assemble in the Royal Capital and are placed under the command of Mereoleona Vermillion. After the squad travels to the Gravito Rock Zone, Mereoleona explains the situation and divides the squad into teams. Yuno infiltrates the dungeon with Klaus, Hamon, and Mimosa. As they make their way deeper, Klaus wonders what one of the defeated mages means by "true forms."
Klaus and his team make it to the central room and discover a figure floating in a sphere of mana. Suddenly the figure shines brightly and Klaus, Yuno, and Hamon begin glowing, too. The three are possessed by elf spirits and turn on Mimosa. Scared and confused, she asks what is happening, but Klaus disapproves of her familiar tone.
After he and Hamon overpower Mimosa, Klaus secures her to a steel cross. Before they can execute her, Rhya drops Asta into the room, and Klaus forbids the boy from trying to free Mimosa. Klaus and Hamon attack Asta, who shouts at Klaus. When Klaus' body reacts, the elf spirit declares that his hatred is stronger than Klaus and Asta's bond. He continues his attacks, injuring Asta. Klaus and Hamon merge their powerful spells, and Asta, refusing to give up, declares that he will be the Magic Emperor. The elves unleash their magic but Yuno destroys it, having been roused by Asta's declaration.
- Creation Magic: Klaus uses this form of magic to manifest any entities that he desires out of steel. Klaus uses this magic to create object composed of steel that could be used for offense and defense purposes.
- Restraining Magic: Klaus uses this form of magic to create any steel-based objects that he could use to restrain his opponent.
- Compound Magic: Klaus combines his Steel Magic with Luck Voltia's Lightning Magic and Puli Angel's Wing Magic.
- Grimoire: Klaus possesses a grimoire that contains various steel-based spells. The grimoire has a light-colored covers with intricate designs on each covers. Additionally, it has the three-leaf clover insignia on the center of the front cover.
- Blood Brothers Reunion
- Declaration of Ascension
- The Undead Invasion
- Star Awards Festival
- Royal Knights Selection Exam
- Klaus' favorite activities are reading and architectural appreciation.
- Klaus ranked 26th in the first popularity poll and 33rd in the second.
- Klaus is the fifth most beautiful man.
- Lunettes is French for "glasses".
- Despite not having been shown being formally introduced to Luck Voltia, he did recognize him when they met in the Dungeon, and knew that Luck had almost killed his opponent. This suggest that Klaus either took his exam at the same time as Luck, or attended Luck's test the same way Finral and Gordon attended with their captain.