Shinmai Maou no Keiyakusha Wiki

I'll kill you a hundred times!

—Mio's catchphrase

Naruse Mio
Mio 01.png
Name Naruse Mio
Kanji 成瀬 澪(なるせ みお)
Rōmaji Naruse Mio
Age 16
Gender Female Female
Hair Color Crimson
Eye Color Pink
Personal Status
Status Active
Relative(s) Ashe (Mother) †
Wilbert (Father)
Ramusas (Fraternity Uncle)
Sapphire (Aunt)
Basara Toujou (Cousin/Husband)
Maria Naruse (Younger Half-sister)
Jin Toujou (Uncle/Father-in-Law)
Unborn Child
Professional Status
Race Demon/Human Hybrid
Occupation Student
Student council
Affiliation Moderate Faction
Hijirigasaka Academy (Second-Year Student)
Toujou Family
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 the main female protagonist of the series. She is the daughter of the previous Demon Lord, Wilbert and a human named Ashe thus making her a humanoid demon, as well as the niece of Sapphire. After the "death" of her father, Mio inherited his power and was raised in the Human World as the daughter of two unnamed demons as a human. Though after the death of her adoptive parents, she was later saved by Maria who revealed the truth about her lineage.

Both later came up with the ruse where their "mother" would be marrying Jin Toujou and become the stepsisters of Basara in an attempt to make their house their base, while father and son would have their memories altered and move elsewhere. However, this plan failed after both of them were revealed to be banished members of the Hero Clan, but Mio and Maria continue to live in the Toujou Household.


Mio is a beautiful young woman shorter than Basara with long crimson hair reaching her waist and pink eyes. For someone her age, she has been noted for having a distinctly slender yet curvaceous figure with enormous, bouncy breasts and sizeable buttocks.

Most of the time, she is seen dressed in the uniform of her school, which resembles a white sailor uniform that has a black collar and black cuffs that has white horizontal stripes, an orange-colored tie hanged from the edges of her collar, a short black skirt that has a single white stripe, long black socks that has a red-colored ribbon around her upper thigh, and a pair of maroon-colored shoes.

Because of the constant Master-Servant Contract, and then the Vow, Mio's has become more seductive and sexy, something that most humans have noticed too, her breasts have started growing more too.


Mm… Ahh, Yah…Don't, Broth- Brother, stop it…

—Mio's nature under the succubus' curse

Mio is shown to be a calm and quiet person, especially around those she isn't close to, but she's rather talkative around her closest friends such as Chika and Shiho. It is noted that she can be rather quick to anger based on the situation, mostly if someone close to her is threatened, insulted or harmed, first shown when she slapped Takashi who didn't understand it was Basara who was suffering more than anyone after the incident from six years prior. Mio can also become enraged if she believes someone important to her has been killed to the point of wanting to eliminate the person responsible herself.

Despite being referred to as a dangerous threat by the Hero Clan, Mio is rather caring, honest and compassionate. She hates lying for the most part to those who have helped her as shown when she and Maria lied to Basara and Jin about their marriage to use their home as a base, even choosing to erase their memories so they wouldn't get involved in their problems anymore. Although Mio attempts to act brave and calm all the most, deep down she is afraid about her current situation since she has lived most of her life as a normal high school girl; however, when faced with danger she won't hesitate to face the challenge.

She soon becomes rather close to both Basara and Jin, who she views as being her family. Mio is more close to Basara who she has shown to have some hidden feeling for, but she acts in a more tsundere manner when it is brought up, but Mio's true feelings sometimes comes out when under the effect of the Master-Servant Contract and she refers to him as "Onii-chan" whenever he does anything perverted to her. She becomes rather jealous when he does anything with other girls such as Yuki and Maria, albeit the former is the result of accidents and the latter being due to the succubus' antics. Due to their constant interactions, she becomes more open about her feelings with Basara reaching the Master-Servant Vow and surrendering herself to him completely.

She appeared to dislike perverts as noted in her initial interaction with Basara who walked in the bathroom when she was in there, albeit their lock wasn't fixed. Mio is also prone to sudden outbursts when faced with inappropriate situations such as finding erotic magazines under Basara's bed (despite Mio herself being on top of him in an erotic position while he slept) or being left at the mercy of Maria's succubus curse. As she continued to be affected by the Master-Servant Pact, Mio has become more open with her own desires to where she doesn't mind doing things with Basara and the other girls.


Mio's adoptive parents are killed.

Mio was born the daughter of both the Strongest Demon Lord, Wilbert and a human woman named Ashe. Prior to his "death", he granted his daughter his power and sent her to the human world to be raised as a human girl under the protection of two demons who would act as her parents in order to keep her from being used by either his enemies or those seeking his power.

As planned, Mio lived life as a normal human girl without the knowledge of her lineage together with her parents. However, it didn't last long as Zolgear found them and killed her adoptive parents right in front of her leaving her traumatized, but Mio was soon rescued by Maria who later informed the confused girl about her heritage. At that moment, she had desired revenge against the one who killed her parents, and Maria started to teach her to use her powers.

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 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 apologizes 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.

Powers and Abilities

"Was the gravity waves that didn't let through created a space distortion? Did it create a barrier of high temperature in the surroundings……!?"

Probably, this is the original power of Naruse Mio. Sleeping in the shadow of Wilbert, was Mio's true nature that cannot be warped by any existence.

—Zolgear describing Mio's own innate power.

Demon Powers

Mio is a humanoid demon born as the daughter of the previous Demon Lord, Wilbert who was hailed as being the strongest demon lord. As she has also inherited his demonic power causing the Hero Clan to view her as a threat to the Human World due to her lack of control over her powers and as the next potential Demon Lord classified as an S- surveillance target. It is further shown as she lost control over her powers upon seeing Basara stabbed right in front of her causing a black hole to manifest, however, the Demon Lord power that she inherited from her father acts as a defensive measure and not to be used herself.

In Volume III, underneath Wilbert's own power, Mio also has incredible latent power, which Zolgear first confused for being his and eliminated his hand. In the tournament against the Moderate and Demon Lord Faction, Mio was shown to be strong enough to fight against a Heroic Spirit alone, then assist Basara, Leohart, and Ramusas fight against Chaos. In Volume XI, she had grown strong enough to be able to fight against Byakko and later Sakumei. Near the end of Volume 11 and forming the Master-Servant Vow, Mio is stated to have the potential to rival that of her father who was hailed as the Strongest Demon Lord.

  • 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 afterward.
    • 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 Master: Having discovered her demon heritage, Mio trained with Maria for six months in using magic, but she still needed Maria's help to form a master-servant pact and complex spells. As a High Wizard, she is able to use a number of powerful spells, most of which required concentration. After training and frequent "subjugation" sessions with Basara, her powers and skills have continued to increase to where Mio eliminated a Heroic Spirit in one attack. As a true testament of her growth, she has shown to be able to combat one of the Four Gods, Byakko alone and later fought against him and Sakumei in Volume 12, after forming the master-servant vow.

  • Elemental Magic: Mio's signature magic. She has displayed great skill in the use of natural elements, she has most frequently used Lightning and Fire.
    • Wind Magic: In order to defeat Byakko in volume 10, Mio uses her wind magic to create a tornado. stirring up magnetite sand and then electrolyzing it to create a powerful electromagnet.
    • Fire Barrier: In her battle against both Byakko and Sakumei in volume 11, Mio was 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.
  • Barrier Magic: Mio is able to create barriers to defend herself against attacks in Volume 2, through using Byakko as a catalyst, she was able to create a barrier capable of shifting dimensions and using even the consciousness of the people around them, thus reproducing the surrounding buildings in the town.
  • Flight Magic: In volume 7, Mio has shown the ability to fly via magic.
  • Hellfire Magic: This is a new magic that Mio developed Post-Master-Servant Vow, which combines both Fire and Gravity Magic. She first used it to destroy the white Qilin and complete the Solomon seal.

Master-Servant Contract (Servant): Despite being the first girl who Basara forged a master-servant pact with, albeit on "accident", Mio has had notable difficulties with it due to being unable to what the pact entails and initial distrust between them. However, after different situations, battle, and her blooming feeling for him, she started to progress and deepen her bond with Basara increasing her overall powers using the contract. Mio soon developed this into the Master-Servant Vow and transferred her Fire Element to him.

Other Skills

Sexual Resilience: As a result of frequent subjugation sessions from Basara, Mio has attained resistance to the aphrodisiac effects of the Master-Servant Pact, meaning that he has to come up with various methods to subdue Mio. However, at the same time, she attained an extremely sexually sensitive body that makes being touched by another person difficult at times.

High Charisma: Being a beautiful high school girl with an appealing body, Mio often attracted unwanted attention from the opposite sex. Though, she used 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 people working on it, and half of the male population of the school followed her.


  • Mio's measurements at the start of the Series: B90-W54-H83(G)
  • Height: 156cm (5'1' 1/2); Weight: 41kg (90 lbs)
  • Her first name Mio (澪) means "Waterway" or "Channel".
    • Her surname Naruse (成瀬) means "To become rapids/Channel".
  • Her catchphrase "I'll kill you a hundred times!"
  • Her weak spots are her boobs.
  • First girl to show her vagina and butt to Basara although it was an accident.
    • She first had vaginal sex with Basara.
    • She also gave her anal virginity to Basara.
  • She has a personal succubus vibrating anal beads (was a gift).
  • Mio is the girl who registers the most number of orgasms in the novel, having reached more than 100 orgasms in the 5 hours that Mio spent with Basara, according to the novel 10.
    • Mio's sexual stamina increases enormously from supporting 9 orgasms in the novel 1 to more 100 orgasm in the novel 10.
  • Despite being experienced with flight magic, Mio is prone to motion sickness when riding roller coasters.
  • After the events of volume VII, Mio's tsundere personality disappears for the most part and she is in dere mode constantly, by volume XII she refers to Basara as "oniichan" in front of other people.
  • She has a fear of cockroaches.
  • She was one of the first four girls pregnant with Basara's child.


Site Navigation