Gash is a short character with short light blonde hair which barely hides two tiny horns underneath and large light orange-colored eyes with destinctive thin black lines underneath them. His outfit consists of a large black/blue cloak held up by a large white bow with a golden yellow jewel and lastly wears blue shoes with white and blue cuffs.
Gash can be described as a happy, but at times protective (sticking up for those who he cares about.) He also (given his age) possess steryotypical child-like tendencies which is mostly for comic relief (which mostly get on the nerves of Kiyomaro, who retaliates by yelling or hitting him on the head.) Gash, like many mamono, has a large appetite as he catches and eats lots "yellow-tail" (he went to extreme lengths to eat everyone at Kiyo's school yellow-tail fish). Also even when he's not eating his favorite snack, he (like many mamono) has a enormous appetite, which is likely due to the fact that mamodo have different body functions than humans, and furthermore from all the fighting they've been involved in. Even though Gash is optimistic and kindhearted he can be quite serious and won't forgive those who hurt (or lay a finger on) his loved ones as shown when Gash and Kyomaro were losing against Bari and Gustav (Gash would even risk his own life to protect Kiyomaro.) Another time was when he heard of how his twin brother Zeon mercilessly sent Rops back to the mamono world and vowed to stop him at all costs (the same goes to Zofis and Clear Note.) In the mamodo world, Gash was looked down upon and was repeatedly called a "weak crybaby" by the other mamodo. Unknown to them, and even Gash himself initially, Gash possess a lot of hidden potential. This would come into play in his battles to become Mamodo King, and he would surprise all of his enemies, many of whom thought that they would easily defeat him. He even learned the ultimate spell Baou Zakeruga that his twin Zeon never had (something which Zeon wanted and envied Gash for.) He has also shown to get in a state of shock or display temporary phobias. An example is when he overheard Sherry and Brago's talk of his existence as a mamodo fighting for the title of "King." Another occurs while traveling to England. He ventured to a forest where he was sent to, only to be reminded of Zeon's presence which frightened him greatly above all else. Gash has been shown to keep his promises, like when Koruru's book was burned she only wished for a "kind king." Ever since then he made a vow to become that type of king though the other mamono that he befriended (with the exception of Brago) never found a flaw/problem with that and they encouraged him to strive towards his goal. He also seems disgusted with people and other mamodo who only make others suffer for their own sick pleasures. Gash shows a strong sense of friendship when he made Kiyomaro open up towards others (more so acting like a brother to him). Another time was when he befriended a dog (which was a mamono anemd Gofure) when he took to the streets after a scuffle with Kiyomaro. He even tried to make friends with Naomi and other kids (which becomes his undoing, being chased by her in her trademark kiddy car) and even saw a best friend connection with Umagon, Suzume, and Kiyomaro's other 3 friends and easily acceped Kyanchome and Tio into the group (and other mamodo like Danny, Wonlei, Kido, etc.) This proves that Gash loves and cares about the people he befriended and does what he can to keep those bonds.
A professor named Seitaro Takamine, finds Gash wounded and unconscious in a forest in England. Seitaro also discovers that the child has no memories of his past, other than his name. When Gash promises to return the favor for saving his life, Seitaro asks Zatch to meet with his son, Kiyomaro Takamine. In doing so he hopes that Gash can help Kiyomaro break certain bad habits, such as skipping school. In turn, Seitaro also asks Kiyomaro to help Gash rediscover his lost memories. Gash is overly cheerful, possessing a strong sense of justice, but is clueless about most the world around him and often gets in trouble when not being supervised by someone. He is also initially unaware of the fact that he can shoot lighting out of his mouth through use of his spellbook. The revelation of that fact, along with finding out that he is a mamono, upsets Gash quite deeply. In an effort to keep Gash busy, Kiyo gave him a "friend" named Vulcan 300 (Volcan 300 in the English). It's in reality a snack box with chopsticks attached, and there's been several different versions of Vulcan 300 (and a burial site for all the previous versions). Gash's favorite food is Yellowtail tuna, which he prefers to eat whole; his favorite TV show is Kamakiri Joe (Praying Mantis Joe in the English Dub) Later on, Gash remembers that after he was transported to Earth, he was lost in the forest until he was found by a mamono who looked just like him - Zeon. Zeon attacked Gash out of sheer, unexplained hatred and then, instead of burning his book, decided to erase his memories of the mamodo world, but he would be constantly attacked without knowing why. Later, when Gash finally battles Zeno, it is revealed that they are twin brothers. Because Gash had been born with the powers of "Baou", the most powerful and destructive of his father's abilities, the king was forced to send Gast far away to live with a caretaker. This was done, then he would not be corrupted and use this power for evil purposes. However, the caretaker that Gash ended up with was very cruel, making him do all of the household chores for her and constantly telling him that he had no family. He was also sent to an academy for demon children, where he would be the constant target of bullies (including Tio) due to his kind and generous nature. After a long and intense battle, Gash was able to defeat Zeon with Baou Zakeruga. It was at this moment that the Baou dragon revealed Gash's harsh past to Zeon, causing him to regret his actions against his brother. As his book burned, Zeon gave Zatch a letter and then transferred the remainder of his power to Gash. When Gash and Kiyomaro returned to Japan, they read the letter, which stated that when the number of demon remaining on earth fell to ten, a "new hell" awaited them. This dire situation would eventually be revealed as the "King Festival" and the threat of the demon known as Clear Note. Gash later becomes a participant in the King Festival, the final battles to determine the ruler of the demon world. Shortly after the event starts, Earth, one of the festival participants and Gash's ally, becomes the first to have his book burned. While visiting Earth's partner Elly in the hospital, Zatch and Kiyo are confronted by the dragon demon Ashuron and his partner Riin. Ashuron tests Gash's skills and reveals the threat from the malevolent demon, Clear Note. He also reveals that Brago and Sherry are currently fighting against Clear. They all depart on Ashuron to try and intercept them. They arrive just in time to save Brago and Sherry from being annihilated by Clear Note. Gash then watches as Ashuron engages Clear in battle, where both sides appear evenly matched. However, Clear soon emerges the victor over Ashuron. Gash steps in to battle Clear, taking over for Ashuron who has been incapacitated. It seems that Gash's cloak is able to deflect Clear's "annihilation" spells, and can be used to protect Kiyo. However, it gives out in the last moments of the battle, although Ashuron intercepts Clear's attack with his own body. Ashuron launches one last desperate attack on Clear at the cost of his body and book, but manages to impale Clear on his head spike. However, Clear manages to survive and is pulled into Goomu's pocket dimension stating that he would be back in 10 months to take them on again. Gash later undergoes training from Zeon's partner Dufort, improving his strength, dodging abilities and learning to control his cloak. The cloak in question has the powers such as high leveled invincibility, teleportation, cloning, and can shape itself to the owners choosing. So far it has shown to be able to spin at high rates causing the user to fly. Aften ten months of training, Gash has grown physically stronger and muscular, can control his cloak at will, and his facial expressions and general appearance looks similar to his brother, Zeon. Before completing their training, Gash and Kiyomaro learn that Purio and Kyanchomé were sent back by Clear. They later encounter Gorm who also is sent back. Shortly after they begin to make their way to the final battleground to face Clear Note. At first they were joined by Tio, Megumi, Sunbeam and Umagon. However, they were constantly attacked by Clear's new spells en route, resulting in both Tia and Umagon's books being burned. With all his friends having now been sent back, Gash arrives to find Clear battling with Brago. Zatch teams up with Brago to battle Clear, while Kiyomaro uses his fully awakened Answer-Talker ability to direct both teams actions. Clear responds by merging with Vino and powering up to an even stronger form and severely injuring Brago. Gash's book glows gold, and the spirits of various mamodo that he had allied with appeared. Kiyomaro is able to use the spells of these mamodo, which had powered up exponentially, and as a result half of Clear Note's body is destroyed. Clear flies off into space and attempts to destroy the planet. The spirits of all the mamodo appear and give Gashh the power to unleash his ultimate spell, Shin Beruwan Bao Zakeruga. Clear Note's body is destroyed and his book burned as Gash and Kiyomaro celebrate with the spirits of his friends. After the spirits of the mamodo vanish, Kiyomaro talks with Sherry and Brago and requests a three month hiatus before they battle. Kiyomaro explains that his graduation will happen soon and wants Gash to be there. Sherry and Brago understand and Kiyomaro returns to school and graduates, with Gash watching. The three months pass and Kiyomaro and Gash face off against Sherry and Brago in the final battle of the King Festival, with the winner becoming the new mamono king. Gash and Brago start the battle with their first spells and the battle commences. The final battle is vicious as both mamodo trade spells and physical attacks. Both mamono sustain injury and the battle appears evenly matched. Both sides decide to risk everything and pour their energy into one final attack; Gash unleashing Baou Zakeruga and Brago countering with Shin Baberu Gubaridon. Brago's spell manages to hold back Gash's attack for a short time, but in the end Baou breaks through. As the attack approaches, Brago reaches back and takes Sherry's hand, causing her to drop the spellbook. Brago thanks her for all she's done for him and she breaks down and cries on his shoulder as his book is set ablaze by the lightning, sealing Gash's victory in the King Festival and earning him the title of Mamono King.
In the aftermath, Gash and Kiyomaro are forced to part, due to the battle for the Mamono King having been completed. Back in the Mamono World, Gash chooses to attend his regular school, not to take on the special privileges that came with becoming the King. Around a month later, Gash and the other mamodo children are given the opportunity to send letters to their former partners, and a picture, if they choose. In the letter sent to Kiyomaro, he claims they will meet again, with or without the books.
- Gash's spellbook is normally red, but temporarily becomes gold in manga chapter 316 and anime episode 149.
- Like all Mamono, Gash has horns; like Tia, they are underneath his hair.
- It is often displayed that Gash has an extremely hard head.
- Also in the original version, Gash often ends his sentences with "(na)no da", an expression of emphasis. He also uses the phrase "Unu" often (usually translated as merely "Yes!"). In the English version, Gash has a notable cadence in his laugh. (Ha ha ha ha haa ha-ha)
- In episode 1, Kiyomaro discovers that Gash has small horns hidden in his hair; however, they have never been seen nor mentioned again after episode 2. A few other demons including Kido and Reira have been seen with horns on their heads.
- The name "Kiyomaro" translates to pure or purity.
- Some sources incorrectly list Kiyomaro's name in the English-dubbed version of "Zatch Bell" as "Kory". An article about the series published in Anime Insider magazine prior to the American premiere of Zatch Bell also called Kiyomaro "Kory," suggesting that perhaps Kiyomaro was originally to be renamed Kory in the English version. In the final English dub, "Kory" is the name of a boy Kiyo and Zatch meet in London.
- In the earlier episodes, Gash has the uncanny ability to locate anything by smell. However, this ability is infrequently used in the later episodes.
- A running gag is that whenever Kiyomaro completely loses his temper his face morphs to look like an Oni's and he produces an incredibly scary aura that freaks out all who witness it (mainly Gash). This normally only happens to Gash, however in the Faudo Arc he assumes that when confronting Zeon's minions and it freaks out Gash, his friends, Zeon, Dufort, and Zeon's minions. He also assumes various demonic faces while casting an array of spells on Rodeaux as punishment for insulting his friends.
- Kiyo appears to be "love sick" with Megumi (The pop idol and Tio's partner.) Evidence of this includes when Mrs. Wriggles tells him to write about being love sick and he whispers to himself, while smiling stupidly, "Love sick, maybe I'll write about Megumi, aw shucks." (English Dubbed Only)
- Kiyomaro blushes many times when talking to Megumi and in episode 57 he seems to be embaraased when he was telling Megumi to hurry up with the books, but he was fine yelling at Gash and Tio.
- Even though Kiyomaro tells Gash and Umagon that they can't come to school with him, they somehow manage to get in the classroom (much to Kiyomaro's embarassment or chagrin.)
- Gash gets easily sidetracked, as shown when Kiyomaro's mother gave him a shopping request, only to be distracted with spying on Naomi with Umagon and Tio, only to come home empty-handed and he then realized that he forgot about shopping (much to Kiyomaro's mother disappointment.)
- Though a Straight-A student, Kiyomaro was rarely (well 0.1% of time) shown failing due to Mr. Toyama's ridiculous tests (mostly out of his sadistic pleasure to see Kiyomaro fail, it almost worked until he literally got suspended) or in Mrs. Wriggles case "love sick" poetry (which he made-up being love sick about breakfast to which Gash came in and told him that's not what he's love sick about.)