Naruse Mio
Mio 01
Name Naruse Mio
Kanji 成瀬 澪
Rōmaji Naruse Mio
Age 16
Gender Female Female
Hair Color Crimson
Eye Color Pink
Personal Status
Status Active
Relative(s) Wilbert (Biological Father)
Ashe (Biological Mother)
Ramusas (Uncle)
Sapphire (Aunt)
Basara Toujou (Stepbrother/ Cousin)
Maria Naruse (Half-sister)
Jin Toujou (Step-father)
Unborn Child
Professional Status
Race Demon/Human Hybrid
Occupation Student
Student council
Affiliation Moderate Faction

Hijirigasaka Academy (Second-Year Student)
Toujou Household

First Appearance
Light Novel Volume I
Manga Chapter 1
Anime Season 1 Episode 1
Voice Actor Ayaka Asai (Japanese)
Lauren Landa (English)
Image Gallery

Mio Naruse (成瀬 澪 Naruse Mio) is a Demon who is the Demon Princess and next in line for the Demon Lord position. She is the daughter of the previous Demon Lord, the late Wilbert, and is the niece of Ramusas. She inherited her father's abilities after his death and became aware of her heritage 6 months before meeting the Toujou family who unofficially adopt her and her retainer, Maria, into their family. Mio became Basara's servant through the Master-Servant Contract.


Mio is a beautiful young woman of short height, with pink eyes. She has long crimson hair that reached down to her waist. For someone her age, she is noted for having a distinctly slender yet curvaceous figure with large breasts. Mio has been seen wearing a number of outfits throughout the series, with several casual attires at home that are usually form-fitting or revealing, as well as a uniform for attending school. After forming a contract with Basara, Mio gains a choker-like tattoo around her throat which takes the appearance of a love heart with two prongs extending around either side of her neck.


Mio normally displays a calm demeanour, preferring to remain quiet when around others. However, she is prone to outbursts when faced with inappropriate situations such as finding erotic magazines underneath Basara's bed or being left at the mercy of Maria's succubus curse. Despite this, she is also caring and affectionate. She genuinely appreciates Basara's kind treatment and protection, and feels uncomfortable about having to deceive innocent people. Deep down she is afraid of her current situation and constantly being under threat, but when faced with danger she won't hesitate to face the challenge.

Originally, when trying to deceive Basara and his father, Mio displayed a personality very typical to that of a teenage girl. While at home she acted like a normal sister towards Basara, waking him up in the morning and referring to him as 'big brother'.


Mio's Adoptive Parents Are Killed

Mio's adoptive parents are killed.

When Mio was born, her father entrusted her to two demons to raise her on earth like a normal human girl in order to protect her from his enemies. However, this plan failed when her father died and her adoptive parents were killed by Zolgear, traumatising Mio and leaving Maria as her only guardian.

A week before moving in with Basara and his father, Jin, Mio and Maria are asked to meet up with the men at a restaurant in order to get to know each other first. Having been unknowingly assigned to the wrong table, Mio goes to the bathroom while waiting. Unfortunately, because of a loose lock, Basara accidentally walks in on Mio while her pants are down, embarrassing her tremendously. Going to scream, the young man quickly muffles her while trying to excuse his mistake, only to result in her slapping him. Before things can escalate, Jin comes to check on his son and reveals that they are the men Mio was meant to meet.

Mio Talking With Basara

Mio requesting Basara's care.

During their subsequent meeting, Mio remains silent as Maria explains their situation, and instead glares bitterly at Basara, only speaking to introduce herself. As the young man tries to excuse himself again, she eventually forgives him once he apologises properly. Thanking the two men for taking them in, Mio then asks Basara if he'll take care of her as well. Promising that he will, she nonetheless warns him to not peek again unless he wants to die a hundred times over.


The Day He Got a Little Sister


Mio's method of waking up Basara.

Having finally moved in with Basara's family, Mio decides to begin the first day as siblings by waking up the young man in the morning, doing so by straddling his lower body as a greeting. Calling it 'a service on the first day of co-habitation', Mio's friendliness quickly turns to outrage as she pulls of the blanket covering Basara, only to find several erotic magazines underneath. Seeing that they all had to do with little step-sisters, Mio accuses him of wanting to attempt lewd acts with them and begins to throw the magazines at Basara. In the commotion, both teenagers lose their balance and fall out of the bed, further angering Mio when Basara comes out on top. Coming downstairs for breakfast, Mio then finds Basara being teased by Maria and wonders if he's 'making a move' on her next.

Basara Riding With Mio

Mio and Basara riding together.

Before leaving for the day, Jin gets the group to take a photo together to commemorate their new family, promising to send the photo to the girls' mother overseas. Basara then takes Mio out on his bike, asking her to guide him around town while they do some shopping. Taking the opportunity to ask him about the dream he was having that morning, Basara vaguely describes it as probably being the result of a trauma he suffered as a child.

After completing their shopping, Basara momentarily leaves Mio to unchain their bike. While he's gone, several thugs take the chance to move in on Mio, trying to convince her to go with them. Returning with the bike, Basara asserts that she's with him, and unhesitatingly strikes one of the men with the front tyre of the bike, surprising Mio. Throwing an open container filled with pepper at them, Basara then grabs Mio and rides away safely. Apologising for causing trouble, Basara assures Mio that it wasn't her fault.

Basara and Mio at Sunset

Mio and Basara at sunset.

Despite his reassurance, Mio remains upset over what had just happened. Suddenly declaring that they're taking a detour, Mio is then taken to an open park with a clear view of the city at sunset. Explaining that he'd heard about this famous spot before moving in, Basara then promises to save Mio no matter what, as it's only natural for families to help each other out. Smiling, Mio tells Basara that he's actually sounding like an older brother now. Before heading back home, Mio takes one last sad look at the scenery.

Mio Says Goodbye

Mio bidding Basara farewell.

Later that night, after Jin leaves town for a business trip, Maria and Mio agree to 'begin'. Basara then re-enters the house after seeing his father off, and Mio remains awfully quiet while Maria asks if Jin has finally left. Finally speaking up, Mio then requests for Basara to leave the house immediately. Before he can respond, Maria uses an invisible force to throw him against the wall, stunning the young man. Explaining that it was magic, Maria transforms into her succubus form before revealing to Basara that Mio is in fact the future Demon Lord. In shock, Basara asks Mio if it was all true. Without any emotion, Mio coldly apologises before saying goodbye as Maria activates her memory spell.

Surprisingly, Basara is unaffected by Maria's memory magic and quickly goes on the offensive, revealing himself to be one of the 'heroes' who oppose demons. Summoning his weapon, the young man goes to attack Mio with Maria jumping inbetween them. Before landing his attack, Basara stops and tells them he doesn't care that they're demons, but asks them to leave due to deceiving him and his father. Without further conflict, Mio and Maria leave the house.

Shadow and Manticores Attack

Mio and Maria being attacked by demons.

Going to the park Basara had shown her earlier, Mio asks Maria that they not deceive anybody any more. However, before they can move on Mio notices that a magical barrier has been erected, and from behind them comes a shadow demon, and two manticores. Commenting that she'll never forgive them for the feud over her parents, Mio promises to kill them a hundred times over as she becomes cloaked in a shroud of power.

Basara Catches Mio

Mio being caught in mid-air by Basara.

Fighting off the manticores and seemingly destroying them along with the shadow, Mio is surprised to see the shadow demon suddenly reform, realizing it had used barrier magic to survive her attacks. Landing a blow, the shadow demon paralyses Mio and sending her flying over the nearby cliff. Wondering if this is how she will die, Mio is then caught out of the air by Basara who had just arrived. Killing the shadow demon with his summoned sword, Basara tells the two girls to forget about before and offers to take them home.

The Way to Conquer Your Stepsister

We Are Family

Mio being reassured that they are family.

Once returning home, Mio takes a bath while Maria and Basara talk in the kitchen. Finishing in the bath, Mio thinks over the past six months as she dries herself off, comparing her first real battle with all of the training she had gone through with Maria. Realising that she would have died without Basara's intervention, Mio grips herself to try and stop the shaking. While dressing, Basara knocks on the door and speaks with her through the wall, apologising for sending them out without thinking. Trying to refute his apologies, Basara deflects her arguments by commenting on how there were quicker, more violent means to remove him from the house, noting her kind personality. Reminding him that the remarrying of their parents was just an act and that they weren't family, Basara simply says that wanting to protect each other makes them family.

The Master-Retainer Contract

Mio participating in the contract ritual with Basara.

Maria then interrupts the moment, snickering about how well the two were getting along. Before Mio can retort, Maria continues on to explain how there may be time when Basara and her are separated, and that while there isn't a magic to perfectly locate someone, they may be able to achieve something close. Revealing it to be a contract magic specific for masters and retainers, Basara becomes uncomfortable about having their souls united and asks Mio if she is okay with it. Mio then responds that she doesn't mind it, surprising the young man. Proceeding to begin the ritual, Maria supports Mio as she begins to cast the spell. Things don't go as planned however, as the mark for the master appears on Basara's hand - sending the two demon girls into a panic. As the mark on his hand begins to disappear, Mio refuses to submit to the ritual despite Maria's persuasion.

Retainer Mark

Mio's retainer mark activating.

Disappearing entirely, Maria comments that this isn't good. As she says this, the mark for the retainer appears around Mio neck and seemingly activates. Concerned for her, Basara reaches over and touches her shoulder, causing Mio to suddenly cry out in seemingly pleasure. Confused by this, both Mio and Basara then listen as Maria explains that it's the result of the 'curse', the effects of the contract should the retainer disobey the master, in this case Mio refusing to submit to the ritual. Due to Maria being the one to cast the spell, the curse would then have the aphrodisiac effects of a succubus, drastically increasing Mio's sexual desire.

Panting, Mio begs them to help her. Telling Basara that she'll eventually die at this rate if they don't do something, Maria explains that in order to lift the curse he'll have to make her obey him by touching her body. Embarrassed, Mio demands to know what Maria is planning, noting the little succubus' apparent delight at the situation. Despite the curse affecting her state of mind, Mio tries to resist the plan until Basara finally makes contact, rubbing her arms. While Mio moans loudly, Maria quietly tips off Basara about Mio's sensitive breasts which once touched quickly sends her into a frenzy. Still refusing to obey Barasa, Maria becomes concerned that the curse won't be lifted and so suggests that he touch Mio's breasts directly, which results in Mio continually crying out 'big brother!'.

Mio Angry with Maria

Mio taking out her anger on Maria.

Eventually, after bringing Mio to the edge nine times, the curse is finally lifted. Left to sleep on the couch due to exhaustion, Mio recovers soon enough and drags Maria away, chastising her over the entire ordeal.

Powers & Abilities

Not only is Mio a humanoid demon, but she is also the daughter of the recently deceased Demon Lord Wilbert, who was hailed as the strongest Demon Lord in history.

Immense Demonic Power: When Wilbert died, he somehow transferred his powers to his daughter, Mio, to insure her safety. Due to inheriting all of her father's powers, Mio is assumed to be capable of doing anything the late Demon Lord could. However, because this power is separate from her natural abilities, and due to her inexperience, she has yet to fully awaken it. She also has extreme difficulty controlling this power when it is unleashed, as shown when she once accidentally created a small black hole than nearly destroyed her and everybody around her.

  • Gravity Magic: The signature ability of her father. Mio is capable of using the same gravity magic as her father, but not to the same extent. While her control of this magic is lacking, it's raw power is still enough to easily crush any opponent, including a Heroic Spirit, albeit leaving her extremely exhausted afterwards.
  • Gravity Barrier: An ability Mio once used without even realizing it. By focusing her Gravity Magic, she creates a concentration of distorted gravity around herself, capable of blocking almost any attack.

Magic Expert: After discovering her Demon heritage, Mio trained with Maria for six months in the use of magic. Initially, her level of competency was of low-level, and she needed the assistance of Maria to perform more complicated spells and enchantments, with varying results of success. After further training, and frequent "subjugation" sessions with Basara, her power and skill have increased drastically, to the point that she could single-handedly destroy a Heroic Spirit in one attack.

  • Elemental Magic: Mio's signature method of attack. She has displayed great skill in the use of natural elements, she most frequently uses lightning and fire.
  • Flight Magic: During the events of volume 7, Mio has shown the ability to fly via magic.
  • Wind Magic: In order to defeat Byakko in volume 10, Mio uses her wind magic to crate a tornado. stirring up magnetite sand and then electrolyzing it to create a powerful electromagnet.
  • Fire Barrier: During her battle against Byakko and the white Qilin Sakumei in volume 11, Mio is forced to form a spherical wall of fire around her body, to defend against the unending assault of Byakko's spears and Sakumei's crescent blades.

Master-Servant Contract Though not one of her own abilities, the Master-Servant contract that Mio has with Basara is still considered a demonic power. As the first person who signed the contract with Basara, Mio has set time aside almost everyday to deepen her bond with Basara and increase her overall power with the contract. As such, her power has grown to the point that even after having the lion's share of her power sealed off by Zolgear, Mio was still powerful enough to blow off his hand just by getting near it.

  • Hellfire magic: a new type of magic Mio develops post Master-Servant Vow with Basara. It's the combination of fire and gravity magic. She first used it to destroy the white Qilin and complete the Solomon seal.

Sexual Resilience: As a result of her frequent "subjugation" sessions with Basara, Mio has acquired a high level of resilience to the aphrodisiac effects of the Master Servant contract. Though at the same time, she's also gained an extremely, sexually sensitive body that makes being touched by another person difficult at times.

High-Level Charisma: As a pretty high school girl with an appealing body, Mio has often attracted unwanted attention from the opposite sex. But, she is able to use this attention to her advantage by getting the members of her fan club to work for her on occasion. For example, during the preparations for the school festival, Mio simply joined one of the departments with the least amount of people working on it, and half of the male population of the school followed her.


  • Measurements: B90-W54-H83(G)
  • Height: 156cm (5'1'' 1/2)
  • Weight: 41kg (90 pounds)
  • Her weak spots are her boobs.
  • Her first sexual intercourse was vaginal
  • She first had vaginal sex with Basara.


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