Karias has long, blonde hair with the usual red eyes of a Noble. The upper part of his noble's attire is quite loose, matching his laid back personality. He wears the Ye Ran Special Security uniform when staying at the human world.
Karias is an eccentric and unorthodox individual even among the nobles. He seeks opportunity to bask in glory and likes to brag about himself - a running gag of the story being Karias proclaiming to be Raskreia's younger brother.
Karias is very cordial towards most women (with the exception of the 5th elder).
Although he appears carefree and happy-go-lucky most of the time, he nurtures deep thoughts regarding nobles and their lifestyle. He shares with Regis his concerns over the nobles being stagnant and dominating others with just power. He believes that Regis and Seira are beings who will bring change to the world of nobles. The previous Lord liked Karias (seeing that his attitude is not like a noble) and thought that he reminded him of his own youth.
Karias Blerster is the son of Krasis Blerster and so succeeded the position after his father had entered eternal sleep. It is revealed that in the past, the previous Lord told Krasis that he should make sure that his son would not become as stiff as him. Krasis took it as a decree and hence, Karias turned out to be quite different.
Karias is sent along with Rajak to capture the leader of traitors and bring him to the Lord. On their way, they see Regis dashing towards the castle. Karias decides to deal with the child and sends Rajak off to capture the enemy. Karias blocks Regis' way and tries to stop him from going to the castle. Unable to convince him with words, Karias strikes a deal - if Regis can land a strike at him, he himself would escort him to see Gejutel.
Carrying Regis to the Room of Discipline, Karias stands in front of Gejutel's vacant cell, wondering what has happened. A guard who comes in is surprised to find them and from this guard, he hears that Kaye has escorted Gejutel to the Lord somewhere according to her order. Karias is placed in a dilemma as he has promised Regis that he'd take him to Gejutel.
By the time Karias arrives at the shrine with Regis on his shoulder, the battle between Rai and the Lord has come to an end and the misunderstandings are being cleared. Then the imprint of the previous Lord appears and clarifies his intention behind entering eternal sleep and bequeathing Rai with Ragnarok. The imprint also comments how bright the new generation is, and singles out Karias as the one who is most like him - knowing how to enjoy life. Despite his eccentricity, Karias doesn't find this particularly flattering, coming from their previous Lord and begins to wonder if there is something wrong with his personality.
Karias is shown again when the Union elders are causing ruckus in the human world and Rai is in worse health condition due to random power usage. He demands to be let go in the human world to help out and shoots arrows from Amore at the Lukedonian barrier in protest.
Karias is finally allowed to visit the human world and he arrives the human world after Ignes has kidnapped Seira. Frankenstein appoints him to house-sit while they go to rescue the noble children. Karias is reluctant but obeys for the Noblesse. Later, Karias saves the trio from Yuri and Mark and frightens them away. He joins the household as well as the Special Security and blends wonderfully with the humans. He even takes the responsibility of watching over the school when Tao decides to leave with Takeo to check on Rai and the others.
The following days reveal Karias having become a popular figure in the school. He joins the trio on their way to meet with KSA when he senses the presence of powerful enemies. Dismissing the trio, he greets his enemies with long distance attacks. After their distance is shortened and Karias meets with his enemies, the 3rd and 5th Elders, they introduce each other and engage in a battle. Although Karias manages to keep up for some time, in the end he is overpowered by combined attacks from the two Elders and ends up an open target for the 5th's lethal attack. However, he is saved just on time by none other than the Lord herself.
Karias joins the RK trio in training during their training camp in Frankenstein's Island. He spars with M-21 to train him to control his werewolf transformation. After the sudden attack of the werewolves, they are compelled to withdraw from training and set off for the city. Karias joins Frankenstein and Seira while the trio has left in the earlier helicopter. By the time, they reach the city, battles are underway but Karias believes that the trio have become stronger and they can face the enemy with their teamwork. They arrive in the battle scenario after the battle is over. Both parties work an understanding between themselves and they return to Frankenstein's house.
The wounded are treated in Frankenstein's lab and Karias and Seira are joined by Rael to watch over them.
Karias is sparring with Rael in the training room in Frankenstein's house when the latter experiences a sudden surge in power. Karias suspects something is amiss and asks Rael to summon his soul weapon. Rael complies and brandishes a complete soul weapon. Karias solemnly tells Rael that something might have happened to Rajak. Their fears are confirmed when Frankenstein relays the news regarding the invasion of Lukedonia. Frankenstein asks Karias to stay back and protect the injured. Karias is indignant that a clan leader should stay back when Lukedonia is under attack but resigns to the arrangement.
Rai and Frankenstein leave immediately along with Muzaka and Lunark after learning that M-21 is being used as an experiment specimen by the werewolves. Frankenstein sends for Karias and Rael who were then training at his island. They reach the werewolf territory just as the warriors power up to kill Frankenstein. Karias fights Braang, while Rael and Frankenstein take on Krano and Dorant respectively. The clan leaders succeed in defeating in their opponents but are horrified to find Frankenstein lying unconscious the bottom of a crater. Dorant fights with both of them at the same time and maintains an upperhand. In the course of the battle, Karias repeatedly asks Rael to leave but the latter remains steadfast. Frankenstein wakes up and resumes his battle with Dorant. This time he overwhelms Dorant but Muzaka prevents him from dealing the final strike. Karias and Rael are shocked at his indiscretion with the former werewolf Lord. Soon thereafter, they encounter Kei and Raskreia.
Regis K. Landegre: Karias has fraternal feelings for Regis. During the confrontation in Lukedonia, Karias attempts to drive Regis away from Lukedonia to save his life. However, seeing his stubbornness in not wanting to flee from Lukedonia, Karias promises that if Regis will be able to hit him only once, he will accompany Regis to see his grandfather and could also help Regis to free him. After the clash between the two, Karias is forced to keep his promise to Regis. After the conflict at Lukedonia, Karias helped Regis by being his sparring partner.
Seira J. Loyard: Karias is shown to have quite affectionate feelings towards Seira. Whether it's because of an individual attention or his exceptional politeness with women, is still unknown. But Ludis' facial expression during the dismal of Karias for being unable to greet Seira with his "warm heart" suggests the latter. However it is possible Rozaria went to intercept Seira instead of Karias because she knew he'd be too soft on her.
As a Noble Clan Leader, Karias is very powerful. He could fight evenly with Lunark and the 3rd Elder, even giving them a hard time despite being double teamed. He easily defeats Braang, a powerful werewolfwarrior and holds his own against Dorant, one of the most powerful werewolves. As leader of the Blerster Clan, he is renowned for having the best detection skills among all nobles, able to detect the enemy's presence from miles away and attack them with great accuracy and power from large distances.
Amore: He possesses a soul weapon that is called Amore. It is a huge bow with a dark color and he uses black arrows that he summons using his aura (spiritual energy). Once shot, the arrow turns into a beam of red energy. These arrows can create lighting storms when fired to sky. The arrows can destroy multiple buildings. Amore can be also used even for close combat.
Arrows: Karias can create arrows made of black aura energy to fire at his opponents. He can also create arrows out of red aura energy that are larger and more powerful than his black arrows.
Karias possesses incredible physical strength, shown when he holds off Regis without even using his soul weapon or his full powers. He is also extremely fast, able to dodge Lunark and the 3rd Elder's attacks while staying on the offensive. During his battle with Braang, he is capable of leaving afterimages when the latter tries to attack him.
As a Noble Clan Leader, Karias possesses an immense amount of spiritual energy (aura). He used his aura to create a force field in his battle against Regis, when Regis used his full strength in one attack. The force field was able to easily block Regis' blast of electricity.