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Kyoichi Yasaka (八坂恭一), the Devil King (魔王), is the main antagonist of the KonoSuba series, and is currently engaged in a war with Belzerg, and by extension the world at large. With the his existence, every single monster that lives in the Parallel World continues to get stronger and stronger.


He is mentioned to be quite old, looking to be around in his mid-100's with gray hair. He generally has a human appearance, save for the noticeable horns on his head. He wears a pitch-black outfit. When his powers are active, his body would emit a black mist that strengthens his allies.


The Devil King is rumored to be incredibly powerful and ruthless, however, it seems that many of the negative rumors may be baseless accusations by the Axis Order members, and according to the Prime Minister of Elroad, he is actually a very sophisticated and reasonable person.

The Devil King tries to act like a final boss, speaking in a formal and haughty manner, and provoking Kazuma with villain speeches, like the one about motivations and "evil" plans. However his coward personality sometimes gets in the way, attacking his challengers before a proper introduction and trying to run away of his fight against the Hero (Kazuma), afraid of his minions would be defeated while he deals with Kazuma.

The Devil King seems to have a personality similar to Kazuma's, as in addition to the cowardly, he seems to be long-suffering, resisting most of Kazuma's insults and provocations, since, like Kazuma with his party, the Devil King already deals with his generals' antics. He is also shameless, willing to beg both Wiz and Vanir to be his generals in a way they couldn't say no.

The Devil King also loves and dotes his daughter, strengthening her and treasuring a handmade handkerchief she made to him as a child. However, he is also willing to transfer his powers and title to her in order to avoid his job of suffer a "glorious defeat" at the hands of the Hero.


He became the Devil King centuries ago, by inheriting the cheat skills of his clan, which includes the ability of power boost his allies, which would be the reason why monsters around the world were growing stronger as the time passes. However he transferred most of his skills to his daughter recently. He usually resided in his castle, which has a powerful barrier protecting it, even being able to withstand the power of the Crimson Demons.

In order to catch up with Aqua, who went all by herself to the Devil King's castle, Kazuma and his party, allied to Yunyun, Mitsurugi and Mitsurugi's party, invaded the Devil King castle. In the midst of the battle, Kazuma, who was by far the weakest member of the group, faced the Devil King by himself. Employing a bit of trickery, the adventurer teleported both himself and the Devil King to the lowest level of the deepest dungeon of the continent. Despite this, he was no match for the Devil King. After apparently being defeated, Kazuma realized that he had one final option left. In a suicidal move, he cast Explosion magic killing himself and ending the Devil King's rule once and for all.


The Devil King is very powerful, though he is noted to be past his prime and not necessarily the strongest in his army, since his main function is hang in back and strengthen his followers. According to Serena, he also transferred most of his powers to his daughter. Like Kazuma, he is a Jack-of-all-Trades, defeating swordmen heroes with a sword and magic users with magic.

Power Boost: The Devil King's primary ability that allows him to control his generals and be the Devil King. Any ally near him gets a massive power boost (making even weak creatures comparable to a Devil King's General), though after transfer his skills to his daughter, the range is limited to those in his immediate presence. He is also able to give permanent enhancements by changing stats: Beldia, for instance, was given high resistance to Holy Magic.

Resistance: He demonstrates resistance to non-enchanted attacks and Eris says he is likely immune to debuffs and instant kill effects. He was able to tank his own Inferno spell without much issue.

Strength: Even in his old age, the Devil King is said to be able to crush an ogre's skull with his bare hands.

Speed: He was able to move faster than Kazuma could see. Even after Kazuma had been buffed twice in speed by Eris and Aqua, the Devil King was still able to keep up with him despite being sealed by Aqua and having an injured leg.

Magic: The Devil King has a lot of Magical Power at his disposal, and had enough mana to keep up with and surpass Kazuma's Manatite.

  • Teleportation Magic:
    • Teleport: Instantaneously transports up to 4 targets to a marked locations. Each user can have 3 marked locations for teleportation.
  • Creation Magic:
    • Create Earth Golem: Creates an earthen golem from the ground soil.
  • Basic Magic:
    • Create Earth: Produces sand or soil full of nutrients. The Devil King's version of this spell was able to create enough earth for a golem that rivaled the size of Kazuma's (which was created using high quality Manatite).
  • Advanced Magic:
    • Cursed Lightning: Shoots a piercing bolt of black lightning.
    • Inferno: Summons enormous flames that incinerate the surrounding area.


  • Although he has a Japanese name, the Light Novel makes it very clear that the Devil King is a native of the Konosuba world, and is not from Japan.
    • This is a subversion of the original Web-Novel. During his final battle with Kazuma, the Devil King revealed that, like the main protagonist, he is a reincarnated adventurer, who went rogue and used the cheat ability Aqua had gifted him to try and take over the world. This not only made Kazuma extremely angry, it also explained why the Gods were so quick to accept Kazuma's original request and send Aqua with him. Everything that had happened to this world was essentially Aqua's fault and the Gods wanted her to fix her mistake.
  • In the novel, his name was translated as "Demon King". In Kono Subarashii Sekai ni Bakuen wo! episodes 4-6, the Devil King is called that way too, being called again as "Devil King" in the following episodes.
  • It is mentioned by Kazuma that one of the main reasons the Devil King is at war with Belzerg is due to the antagonization by the Crimson Demons and the Axis Order. However, this may possibly be a joke.