Another horse mamodo like Ponygon, Karudio was first introduced as a rival for the fire horse. At some point in the past, the team was ambushed by two allied Mamodo named Snail and Maraion, taking turns to attack Karudio, which they felt was not right. Although Karudio and Sauza defeated the two mamodo, the battle left them with a negative prejudice regarding "teamwork" and they are highly hesitant to work with others.
Karudio and Sauza's first meeting is shown to be when Karudio came upon Sauza's campsite on Mongolia and Sauza attempted to ride him. Karudio tried his best to unbuckle Sauza but Sauza held on tightly to his mane, tearing out a fistful of his mane on accident. While it is not shown, it can be speculated that Sauza managed to tame Karudio after much effort and became his bookkeeper as well. Despite being animal and human, the two shared a close relationship and Sauza is very fond of Karudio.
Like Ponygon, Karudio also only speaks in animal sounds (Paru Paru Moon), yet Sauza knows his real name. Karudio is one of the few mamodo who can understand Ponygon and knows his real name. During their first confrontation in Hokkaido, Sauza mocked Ponygon's reliance on his allies after Karudio smelled their scent on Ponygon. Kafk Sunbeam, Ponygon's bookkeeper, arrives shortly after and they start battling. The fight is even until Sauza uses "Dio Gikor Gidoruk", granting Karudio an ice armour and the ability to manipulate ice. With his new ability, Karudio easily breaks Ponygon's armour and proceeds to attempt to burn his book. However, Ponygon grabs onto Karudio's hoove, refusing to let them go on and Sunbeam uses this as a distraction to escape in hope of being able to buy some time for restoring his strength from within but Karudio freezes his legs, rendering him immobile. Karudio kicks Ponygon away and reaches towards Sunbeam for the book but Ponygon grabs onto his hoove again and his determination to return home safely to Zatch, no matter what, earns him his third spell, "Dioemur Shudoruk". Sunbeam starts reciting the spell but Karudio engulfs him with an icy wind in hope of halting him from chanting the third spell. Convinced that they had won, Sauza and Karudio goes to burn Ponygon's book but suddenly realize that the snow around them was thawing. They then turn around and see Ponygon emitting flames from his body. The new spell grants Ponygon a new armour and the ability to manipulate flames but Ponygon's inexperience with his new spell causes Sunbeam to end up getting hurt by his flames and Karudio and Sauza uses this to their advantage by attacking Ponygon whilst he steers his flames away from Sunbeam. A weak Sunbeam advises Ponygon to concentrate on the enemy and flare all his fighting spirit at them, further adding that they fight with heart, not technique. Karudio lands another blow on Ponygon, causing Ponygon to collapse. Ponygon then remembers Zatch and his friends and stands up again but Karudio angrily strikes him. Ponygon then remembers Sunbeam's advice and flares all his fighting spirit towards Karudio. Ponygon unleashes a fire clone at Karudio and Sauza to distract them while he escapes with the unconscious Sunbeam but Karudio and Sauza, though surprised at his ability to do so, figures out his trick and tries to attack him. Ponygon blocks their attack with a wall of flames without injuring Sunbeam, which shocked Sauza, since he and Karudio had spent half a year lerning to use their power to that extent. Sauza commands Karudio to pursue the duo but Karudio hesitates and admits to Sauza that he had been afraid of Ponygon's eyes and was thus, tricked by Ponygon's fire clone completely. Sauza realizes that they had lost this time but vows that next time, they would defeat Sunbeam and Ponygon.
In the Faudo Arc, Sauza and Karudio appear again along with Arth and Ellie when Momon, Zatch and Ponygon carry their sleeping bookkeepers to the room in which the device that will send Faudo back to the mamodo world is kept. Arth states that he and Sauza will eliminate all that stand in their way and proceeds to eliminate the group. Sauza immediately uses "Diogikor Gidoruk" and sends an icy wave to the sleeping bookkeepers but is intercepted by Momon's "Ora Norojio". Karudio and Sauza then start battling Sunbeam and Ponygon whilst Zatch and Kiyo try to reason with Arth. Kiyo uses "Rauzaruk" and Zatch manages to defend himself against Arth's sword. Zatch tries to persuade Arth to allow them to use the device but Arth triumphantly revealed that he had already activated the device that will send Faudo back to the mamodo world. Sunbeam angrily asked Arth if he was selfish enough to sacrifice the victims of Riou's curse but Arth pulls away his cloak to reveal a cursed Ellie, angrily stating that sending Faudo back to the mamodo world before his seal was broken was entirely Ellie's decision. At this point, Sauza is notably upset, showing that despite agreeing to aid Ellie in her plan, Sauza is still against her decision to end her life in order to save the world. It is assumed that Sauza has a crush on Ellie because he was very worried about her when she was in pain due to Riou's curse. Kafk mocked Sauza saying "I thought you didn't like working with allies." Calling a truce with Zatch's group, Arth and Karudio ran off to protect the device in Faudo's chest to send him back to the Mamodo world. They get into a fight with the Heart Guardian all the while defending the device. The battle proved difficult, partly due to Karudio's refusal to work in synchrony with Arth. After much convincing from Ellie, the battle took a better turn until the monster organ utilises his fire abilities. In the end, Karudio launches a suicide attack on the Heart Guardian by freezing from the inside out using his strongest spell Diō Gikorio Gidoruk. Karudio survived the attack however, as Sauza allowed one of the Guardian's flames to strike their book prior to the attack, allowing Karudio to return to the mamodo world before he becomes completely frozen.
After Karudio had returned to the mamodo world and Faudo had been stopped, Sauza returns to his home, which appears to be a campsite, where it is believed, that he is reunited with his sister.
Japanese Name: Diou Gigorio Gidoruku (ディオウ・ギゴリオ・ギドルク)
Description: A strengthening spell which bestows Karudio with a new ice-based armor upgrade.
Karudio's spells are variations of Ponygon's Spells. The "Shu" in Ponygon's spells is replaced with "Gio". Instead of the "Emur" in "Dioemur Shudoruk", Karudio has "Diogikor Gidoruk". However, the Doruk ending always remains the same. Both of their second spells begin with Go. Their third spells both begin with "Dio"