Protagonists

Main party

• Hamel - The 18-year-old main character. A traveling hero who uses a violin - as big as a double bass - and magical music to fight his enemies. He can be very rude, perverted and cruel, but he loves his friends and family. When his demon blood awakens, he becomes a powerful Mazoku. He is the son of Pandora and the Demon King Chestra.
• Oboe- Hamel's constant protector and companion, a crow. In time, it turns out that he is a former general of Chestra - more specifically, the former Falcon King. During his time as the Falcon King, Oboe was considered even more powerful than Bass and possessed a power that rivaled that of the Demon King Chestra.
• Flute- The 16-year-old female protagonist who grew up in the small mountain village of Staccato. She is the heiress to the throne of Sforzando and the daughter of King and Queen Horn. She is able to use heal magic - an ability that appears later in the plot - and create barriers. The drawback is, when she uses her magic her life span shortens.
• Raiel- A childhood friend of Hamel. He is the only human friend Hamel had as a child and the first-person Hamel trusted other than his mother. By coming into contact with Pandora's magical music as a child, he was enabled to summon spirits by playing his golden piano; a memento of his deceased parents.
• Trombone- Usually referred to as Trom. The prince of the ruined land of Dal Segno. He is the youngest main character and an excellent swordsman whose main attack is the scissor slash. He and Hamel are often at odds with each other, although they have similar personalities.
• Sizer- The leader of the airborne falcon army of demons, who is later revealed to be Hamel's younger twin sister. Unlike her brother, she looks like an angel with blood-red feathers rather than a human with demonic features. She uses a giant scythe in battle and can summon Valkyries with magical music using her scythe, which she plays like a flute. She was kidnapped by the Mazoku as an infant and raised to be hostile towards humans. In the course of her encounters with her brother, she betrays the Mazoku and joins Hamel's group to redeem herself.
• Ocarina- Sizer's servant, who often takes the form of a crow and has a scar over her right eye. In later chapters it is revealed that she is the daughter of Oboe, and her true form is that of a winged woman. She was Sizer's only companion when she was growing up. She took care of her after every battle and comforted her when she was lonely and sad.

Sforzando

• Queen Horn- The Queen of Sforzando and the mother of Flute. She is wise and compassionate - even if she loves her daughter to an unusuall strong degree - but her health is poor because she uses her healing magic too often. She is also the mother of Lute, the "Demon of Sforzando" who fell into the power of Bass, the King of Hell, many years ago and whose loss she mourns.
• Clarinet- A man in his 20s with long golden hair who is the High Priest and Commander of the Magic Corps. He is currently the most powerful magic user in the world, surpassed only by the power of the Sforzando family line.
• Percuss- One of the ministers of Queen Horn. A middle-aged man with a monocle and a very skilled magician who is very suspicious of Hamel.
• King of Sforzando- The nameless, deceased king of Sforzando, who appears only in a flashback. He is used almost exclusively as a comedic diversion, since everyone - including his wife and son - often forgets who he is.
• Cornet- The younger sister of Clari. In the manga, she has a huge crush on Hamel and tries everything to get rid of Flute as a romantic rival. She is also very spoiled by Clari. Later in the series, she unintentionally transforms into a Mazoku- like creature. In the anime, she is a very straightforward character who is loyal to Queen Horn and has a close relationship with Trom.
• Lute- The elder brother of Flute. He was once called the "Demon of Sforzando" and was greatly feared by all Mazoku, while admired and loved by all people. Shortly after Flute's birth, the kingdom was attacked. Lute sacrificed his life to save his family, but fell under the control of Bass.

Antagonists

The demon army that wants to revive Demon King Chestra by opening Pandora's box. They are immortal as long as they are not killed or consume all their energy. They try to free Chestra, who radiates so much power that they can live off it indefinitely.

• Hell King Bass- The supreme general of the demon armies and leader of the army of the undead. His body has been reduced to his head, but he has taken possession of the body of Flute's brother Lute. He has immense magical powers and is feared by all who serve under him.
• Dragon King Drum- The head of the Dragon Army, an ogre-like monster with two heads. He was eventually killed during the invasion on Sforzando. Famous for his physical strength and his stupidity.
• Warrior King Guitar- The 4th General of Hameln is a centaur-like, canine being: his upper half is an anthropomorphic dog and his lower half is a greyhound with hooves. He uses a variety of mystical swords and is a cunning schemer, but very cowardly.
• Orgel- (Clown of Hell) His appearance is that of a masked jester with a very exaggerated costume. He is one of Bass' special servants in the undead army. He torments his targets with psychological warfare, can bring the spirits of the dead to life and is a master of powerful illusions.
• Vocal- A wild, arrogant demon who rebelled against the authority of Chestra. Because of his actions, he was imprisoned for five hundred years, but is later released so that he can provoke Hamel to awaken Chestra. His full power was sealed by Bass, but he is still immensely powerful, strong and fast; even Bass fears him.
• Pick - Pick, seen only in flashbacks, was once the 3rd warlord of Hameln, upholding the laws and commander of the devil's army. He was slain by Lute years ago before he himself fell.
• Demon King Chestra- The pun on his name comes from the Japanese word for "king," namely "ou." Hence, "Ou Chestra" ( Orchestra ). He is the father of Hamel and Sizer, and as his title indicates, he is the king of demons.

Other characters

• Pandora - The woman who opened a box that released misery into the world. Therefore, the box was also called "Pandora's box". She was a kind and caring woman who loved her children, but sometimes fell victim to a paranoid distrust of others because of the condemnation she experienced. In a flashback, it was revealed that she opened the box for the sake of her children, as they were being held hostage and she had no other choice.
• Vi Olin (Introduced in Movement 26) - The inventor of Hamel's giant magic violin and the creator of Pandora's Box, in which the Demon King Chestra and his minions were imprisoned. He also created the sword that can cut through anything, which ironically was used to cut the lock of Pandora's Box. In Chapter 128, it is revealed that he is the grandfather of Sizer and Hamel, Pandora's father. It is also revealed that he is an angel, which explains Sizer's wings.

Characters

• Shchel - A boy saved by Clari 10 years after the war. He enters Sforzando's school of magic, hoping to become a magician like Clari. He seems to be hiding dark secrets about his body. It seems that he cannot perform magic without Piroro's permission. The secret about his body might be related to the dark fairies.
• Piroro - A fairy in company with Shchel. She seems to abhor great things. It seems that just before her meeting with Shchel, she was forcibly abducted from her home and accompanied him.
• Great - (Alternate spelling: Grate.) The son of Hamel and Flute, who seems to resemble his father in both appearance and personality. Like his father, he can play the violin with magical music, though not yet as well as Hamel. He has also attended the magic school of Sforzando. He has inherited the blood of the demon king Chestra, which causes other demons to bow to him out of respect. This leads Great to have a childhood similar to Hamel's. Although he seems to take a cold attitude towards his family and strangers, he does so out of fear of hurting them. Shortly after meeting Shchel, he opens up.
• Lute - The son of Hamel and Flute, the elder brother of Great. He resembles Flute's brother, Lute. He is also the captain of the Kuu Crusaders, the group of the strongest cadets in the Magicorps. When Lute tries to help Shchel with his magic, he is one of the first to notice the strange and dark aura around Shchel.
• Gospel - A classmate of Shchel and Great, a shaman from the spirit land, Dotar. He uses skulls.
• Count Ridge - A classmate of Shchel and Great, from a family of merchants rumored to be vampire aristocrats.
• Bonshou Rei - A classmate of Shchel and Great, he looks like a jiangshi. He has a divine beast: a tiger named Kayagumu. After being beaten up by Great, he leaves the school and returns to his country.
• Tinor Sax Bone - A classmate of Shchel and Great, a swordsman from Dal Segno. He can summon demon dogs with his black sword. He blames the Mazoku blood for his father's disability and the strange disease his mother carries (based on his family name, he could be the son of Trom Bone and Corrnet).
• Biyorne and Blanche - Classmates of Shchel and Great, a pair of warrior sisters known as the String Sisters. Blanche seems to have a crush on Shchel. Biyorne is responsible for keeping her sister safe. Biyorne wields a giant ax, while Blanche wields a giant hammer.
• Ocarina - The daughter of Raiel and Sizer. She can play the flute to summon little Valkyries. She is also the cousin of Great and Lute. It seems that her growth is accelerated by the angelic blood inherited from her mother.
• Harmony - A girl with butterfly wings and a double-edged scythe. She is currently a member of the Poison Moths of the Fairy Kingdom. Her insignia is carved on the tip of her scythe. She may be the mistress of Shchel. She wears both Shchel's ring and his mother's ring.
• Si and Chest - Hamel and Flute's son.
• David
• Snow Drop Kiy and Elect