All spoilers regarding Volumes 1 through 7 are unmarked.
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Demon Lord Wilbert
- Actual Pacifist: He's the one who initiated the truce between the Demon, Human, and celestial realms.
- All for Nothing: He hid his daughter among humans to keep her safe from rival demonic factions who hated the truce. His death made all that meaningless.
- Daddy Had a Good Reason for Abandoning You: He hid his daughter Mio among human parents so she wouldn't be targeted as either a hostage or assassination target. Unfortunately, his death transferred his power into her and living like a normal human girl, she had no way of knowing how to handle it, thus making herself a beacon for hostile demon factions.
- Death by Origin Story: He is killed by Leohart before the beginning of the story.
- The Ghost: Although his name is often mentioned in passing, he never makes an appearance, not even in flashbacks, although numerous portraits of him do exist, and he gets illustrations.
- The Good King: During his tenure, many of the downcast, discriminated, and decidedly thin-blooded demons finding their way to the Demon world, most who long ago lost many humanoid traits, found acceptance and equality in his domain and loved his rule as a direct result.
- Maligned Mixed Marriage: While the Demon Moderate faction loved him unreservedly, and for good reason, his wife, and Mio's mother was not viewed kindly. With him being a pure-blood noble, and her coming from Earth, raised as a human, she had to live in a tower most of her life, for her own safety, the simple pleasure of tending a flower garden being her only joy.
- Posthumous Character: He's long dead before the story begins.
Mio's birth mother.
- Death by Childbirth: She died very shortly after Mio was born.
- Death by Origin Story: Ashe dies after giving birth to Mio.
- Maligned Mixed Marriage: While her husband, Wilbert, was loved by the Demon moderate faction, she was not.
- Posthumous Character: By the time the story begins, she's already dead.
- Strong Family Resemblance: According to Ortega, Mio's a spitting image of her.
Maria's older sister, Rukia serves as Ramsus's maid and assistant in the moderate faction.
- Adaptational Heroism: Rukia is much more sympathetic in Burst compared to her light novel counterpart. Most notably, she has a larger role in the fight with Nebra and Gald's "heroic spirits."
- Attempted Rape: In the first half of Volume 7, after Zest joins Basara's harem, but before Basara's team goes off to Face Leohart in the tournament, she's overcome by both lust and envy due to the fact that Kurumi is Maria's "toy"... er "special friend", and uses magic to both shred Kurumi's clothes and pin her to the ground before sexually forcing herself despite Kurumi's protests. The only reason she stops is that Shella shows up and calls her daughter out for her actions at Basara's behest.
- Big Damn Heroes: She rescues Maria from one of the "Heroic Spirits" that were attacking Wilbert's domain.
- Didn't Think This Through: Shella points out, in explicit detail, everything that would have gone wrong had Rukia gone through with her threat to kill Basara for complaining about Ramsus's actions towards Mio. Ramsus and Rukia aren't fazed by this at first.
- Easily Forgiven: The only reason she gets any leniency in her sexual assault upon Kurumi is that the Demon Moderates faction is desperate for fighting power due to the persistent threat of the Demon Lord and Demon Council factions. Under any other circumstances, she would have been flayed alive, and that's under her own standards, no less.
- Flight: She can fly in battle.
- Foolish Sibling, Responsible Sibling: She's the responsible to Maria's foolish. While Maria gets things done by teasing and tricking people into doing things her way, Rukia is very calm, composed, strict, and straightforward. Neither of them fully discloses their motives and objectives until they've all played out, however.
- Jerkass Has a Point: While it may seem cruel to inflict punishment upon Maria after what she endured in fighting Zolgia, Rukia's assessment that Maria's crushing guilt for betraying Basara would have been worse proves true when we later see Zest going through a similar crisis of faith.
- Jerk with a Heart of Gold: In spite of her cruel actions, she cares for her mother and younger sister.
- Meido: She both looks and acts as Ramsus's maid.
- My Master, Right or Wrong: She puts the well-being of Ramsus first and foremost.
- Number Two: To Ramsus in the moderate faction.
- The Stoic: She doesn't show any emotion regardless of what's going on around or in front of her.
- Strong Family Resemblance: She greatly resembles her mother and sister, at least in appearance.
- Teleporters and Transporters: She not only opens the gate between the human and demon realms but brings Basara and co. along for the ride.
- Winged Humanoid: She sports wings when she goes into battle.
The leader of the demon's "moderate" faction.
- Adaptational Badass: In the original light novel, Ramsus had to struggle to take down one "heroic spirit" and risked his life by using his Gravity Master powers. In Burst he crushes one into a marble without breaking a sweat, by simply pointing his open palm at it and closing his fist.
- Adaptational Heroism: While Ramsus isn't a villain by a long shot, Burst notably has him pull a Big Damn Heroes moment to help save the demon realm from Nebra's attack.
- All for Nothing: His plan to extract Mio's power is rendered void when Mio decides not to succeed her father.
- Authority Equals Asskicking: He's the leader of the moderate faction and is a capable fighter.
- Badass Baritone: Both Tessho Genda and Christopher Corey Smith provide a deep, booming voice of Ramsus.
- Badass Beard: He has a red beard and can kick major ass when he needs to.
- Badass Cape: He wears a red cape as a part of his armor.
- Because Destiny Says So: He views Mio's powers as this, given that she is Wilbert's daughter; Basara, understandably, doesn't take this well. It's eventually subverted when Mio decides not to succeed her father.
- Big Damn Heroes: He pulls an epic one at the conclusion of volume 7 which results in Chaos being killed by Basara.
- Curtains Match the Window: He has red hair and red eyes.
- Didn't Think This Through: Basara points out the consequences of the fact that Mio was under-protected in the human realm to Ramsus as part of his complaint regarding his actions. Ramsus, however, wasn't fazed at first.
- Gravity Master: He can manipulate gravity at will such as when he helps Basara finish off Chaos in volume 7.
- High-Class Glass: He wears a monocle at all times.
- Horned Humanoid: He has horns just like most of the demons.
- Jerk with a Heart of Gold: In spite of attempting to extract Mio's powers, Ramsus is kind and a good leader who's capable of being selfless; he learns to see good qualities in Mio and gives up his resentment.
- Knight Templar: Ramsus believes in upholding the peace of the demon realm, even if he intends to extract Mio's demon power so that she can live a normal life. Fortunately, he calls it off following Nebra's assault.
- Lack of Empathy: He initially doesn't care that much about his niece's well-being in extracting the latter's powers. Basara, understandably, calls him out on this.
- The Needs of the Many: Ramsus's justification for extracting Mio's power is that by doing so, she could live a normal life. After seeing Mio take to the front lines and risk herself for the people, he calls off his plans.
- One Degree of Separation: Ramsus is Mio's uncle, being the brother of Wilbert.
- The Reveal: By the end of the series, it turns out that his true identity is Wilbert himself.
- The Resenter: He resents Mio because the latter inherited Wilbert's power instead of himself, and considers her unworthy of her title or inheritance. No wonder Basara's so upset with him. Fortunately, Ramsus gets better.
- Shoot the Dog: He views extracting Mio's demon power as this, given that she inherited these powers from Wilbert. Basara disagreed.
- Sour Prude: At first, he thinks that because Mio's in Basara's Master-Servant pact and has a healthy almost sex-life, she isn't fit to rule.
- Staff of Authority: He walks around with an ornate staff.
- Strong Family Resemblance: He's the spitting image of Wilbert, which Basara notices immediately.
- Took a Level in Kindness: After witnessing Mio's prowess in helping her allies fight off Nebra, he finally lets go of his resentment towards his niece.
- Underestimating Badassery: He underestimated how powerful Mio would be and how she would be willing to risk her life for her family.
- Unwitting Instigator of Doom: Him summoning Mio to the demon world gives Leohart the justification he needed to attack the moderate faction, by calling it a clear act of aggression. He even laments his actions while discussing the matter with Jin.
- Well-Intentioned Extremist: Ramsus takes extreme measures to ensure that Mio can live a normal life as a human. That is, until Mio decides not to succeed Wilbert.
- Would Hurt a Child: His plan to extract Mio's demon powers can potentially harm his niece.
- Bathtub Bonding: She joins Basara in the bath to introduce Zest for the purpose having Zest enter a Master-Servant pact with him. Being Maria's mother, it shouldn't surprise anyone that she exploits it for her own amusement.
- Crouching Moron, Hidden Badass: She acts goofier than Maria, but she's clearly a force to be reckoned with if she can make her daughters stand down just by showing up.
- Cruel and Unusual Death: Subverted. Zolgia blows her up with a microwave weapon, but he just killed one of Lars's puppets.
- Damsel in Distress: She is taken hostage by Zolgia near the end of volume 3 in order to force Maria to turn Mio over.
- Disney Death: She is thought to have been killed by Zolgia, but it turns out to be Lars's puppet].
- Fastball Special: In the light novel, she once throws Maria at Rukia while pranking the latter.
- Horned Humanoid: She's got prominent purple horns.
- Mama Bear: She's protective of her daughters as well as Basara.
- Mum Looks Like a Sister: She and Maria have very similar appearances akin to that of twin sisters.
- Nerf: It is revealed that Maria's birth cost her over half her former power. She used to be the first succubus to have enough power to be called a Demon Noble.
- Noodle Incident: How Zolgia captured her is never made clear.
- Power Perversion Potential: She loves to teleport into Basara's lap.
- The Prankster: She's the one who taught Maria everything she knows about pranking people.
- Strong Family Resemblance: She looks and acts very similar to Maria. Rukia is clearly the odd one out in the family.
- Supernatural Is Purple: She has purple horns, purple eyes, and dresses herself in purple from head to toe. She is clearly supernatural as a succubus, and a powerful one who can make her daughters stand down simply by showing up.
- Teleporters and Transporters: She can teleport around. The reason she didn't teleport out of Zolgia's cage is that it was booby trapped and had to be disarmed before she could leave.
- There Was a Door: She prefers to teleport into a room, even when the door is unlocked.
- Trickster Mentor: Like Maria, her lessons are truly for the benefit of her students, but her primary consideration is her own amusment.
- You Have Outlived Your Usefulness: Gets blown up by Zolgia for Maria failing to stop Basara. Subverted when it turns out Maria's mother was still alive, and the thing that blew up was a puppet Lars created.
An elderly demon that used to be Wilbert's top strategist.
- Horned Humanoid: Like the vast majority of demons, he has horns.
- Miniature Senior Citizens: He is amongst the shortest of the demons shown, and he appears quite elderly.
- Mr. Exposition: He explains to Basara's group the current situation in the demon realm, especially the movers and shakers.
- Retired Badass: He was the top strategist for Wilbert long before the latter's death.
- Skunk Stripe: Inverted. He's got one red patch of hair, surrounded by a sea of grey.
- The Strategist: He used to be Wilbert's top strategist.
A maid who is tasked by Claus with giving Mio and co. a tour of Wilbert's lands and people.
- Cute Little Fangs: When she smiles, a little fang can sometimes be seen.
- Genki Girl: She's especially happy and energetic.
- Hair of Gold, Heart of Gold: She's blond and seems to be a good and decent person.
- Large Ham: She has an exuberant and boisterous personality.
- Meido: She's a maid working in Wilbert's castle.
- No Indoor Voice: She nearly blew Mio's cover in maid outfit by being too loud, but she's so excited she just can't help herself.
- One Degree of Separation: She grew up in the same orphanage as Lars.
- Pointed Ears: Like most demons, her ears are pointy.
- Skinship Grope: When she and Mio are in a Furo Scene, the first thing she does is grope Mio rather aggressively while licking her lips lecherously, using the "it's my duty to bathe you" as an excuse.
- This Cannot Be!: When she sees Lars fighting on Leohart's team.
A demon florist frequented by Noel.
- Gentle Giant: He's noted to be a big, burly guy, but he's very gentle and kind, especially as tending flowers requires a very gentle touch.
- One Degree of Separation: He used to deliver flowers to Ashe, Mio's mother.
- Spanner in the Works: Being close to Mio's mother, he saw through her disguise immediately.
- You Remind Me of X: He flat out tells Mio how Mio looks exactly like Ashe, her mother.