Kiyo and Zatch were based on the design of a normal high school student and a noble knight who combats evil.

[4] His next idea was a story where a middle school student, the prototype of Kiyo, finds an old toy and with the help of a noble knight, combats evil.

His intelligence makes him a target for teasing and harassment causing him to develop an introverted and apathetic demeanor to the point where he skips school on a regular basis.

[8] Kiyo still has a disturbingly bad temper and is easily irritated, often venting his frustrations on Zatch or his ditzy classmate Suzy Mizuno.

Zatch is an overly cheerful boy who possesses a strong sense of justice, but is clueless about most of the world around him and often gets in trouble when not being supervised by someone.

During the battle within Faudo, Kiyo gained an ability called Answer Talker (アンサートーカー, Ansa Toka) from being killed and subsequently brought back to life.

[11] Using the ability of Answer Talker in battle allows Kiyo to completely understand an opponent's attack, how to evade it, and how to effectively counterattack.

[12] Zatch's primary offense at first is the spell Zaker (ザケル, Zakeru), which causes him to fire lightning from his mouth.

Rashield (ラシルド, Rashirudo) erects a giant shield that reflect attacks back to the source while also adding electricity to the reflected attack,[19] Jikerdor (ジケルド, Jikerudo) creates a ball of electricity that magnetizes anything following immediate contact,[20] Rauzaruk (ラウザルク, Rauzaruku) amplifies Zatch's physical attributes,[21] Zagurzem (ザグルゼム, Zaguru Zemu) to guide and increase the powers of Zatch's electrical spells,[22][23] and Maazu Jikerdon (マアズジケルドン, Maazu Jikerudon) generates a huge ball of electricity capable of deflecting attacks and attracting the enemy into its epicenter where they are electrocuted.

[32] As they progress inside Faudo, Kiyo is killed in battle but is resuscitated into a catatonic state by Zatch.

[35] Kiyo awakens and with Zatch battles and defeats Zeno and sends Faudo back to the Mamodo World.

Some time passes and Zatch sends Kiyo a letter telling him the peace of the Mamodo world.

[38] Kiyo and Zatch are the protagonists in the two spun off animated films Gekijou Ban Konjiki no Gash Bell!!

[42][43] IGN's review of the first two Tankōbon of the series stated that Kiyo was not a likable character due to his abrasive attitude.

[46] Debi Derryberry was nominated for "Best Actress in a Comedy" for her role as Zatch at the 2006 and 2007 American Anime Awards but did not win.

[47] Since the series was released, merchandise based on Zatch's appearance has been made such as plush toys[48] and action figures.