|Spoiler Alert: This page contains spoilers. Read at your own risk.|
|“||I owe my life to him, and all I have and all I am belong to him alone.||”|
—Miyuki, Volume 5, Summer Break
Shiba Miyuki (司波 深雪) is the main female protagonist of the "The Irregular in Magic High School" light novel and animated series. She is the biological sister of the main protagonist, Shiba Tatsuya. She is a student of First High School.
The spin-off manga, Mahouka Koukou no Yuutousei, has Miyuki as the main protagonist, depicting her point-of-view in a timeline parallel to when the original manga started.
Appearance and Personality
|“|| There is no way I am lacking in my pigmentation. It’s just that my hair is a shade of black too deep.
Could it be hereditary? But, my family line is not supposed to be intermingled with Europeans for the past five generations...well, since I do not know any farther than that; the possibility that this comes from some long ago genetic ancestor is not nonexistent. However, even Okaa-sama becomes a little darker in the summer and Ani’s complexion could be called tanned, since it so splendidly soaks up the sun so much that I can no longer tell what his original color is, so I do not believe it could be called a hereditary thing.
—Miyuki contemplating her appearance and genes, Volume 8, Chapter 2
Miyuki is described as a lovely, beautiful girl who captivates whoever sets their eyes on her. Her arms and legs are slim, slender without looking too unhealthy. It was mentioned by Mayumi that the number of perfectly symmetrical features in Miyuki was overwhelming to the point that "her confidence in herself wavered." This might be caused by her magic prowess which is very formidable and greatly balanced. Miyuki has noted that her features are not entirely similar to that of her family. One funny thing to note is that her figure has become more defined and curvaceous over her first two years at Magic High and has grown large breasts.
Because of her openness, modesty, well-brought up manners, and behavior, coupled with her lovely, beautiful appearance, Miyuki is popular not just among male freshmen students of their school, but also among females and upperclassmen, and even to magicians from other schools and outsiders that may or may not follow the Nine School Competitions' news.
Outsiders or strangers will normally be rendered speechless or flustered by her presence. Her speech and movement patterns are completely different from Tatsuya's, something their deceased mother should be given credit for, and she is referred as a real Yamato Nadeshiko which is a Japanese term meaning the "personification of an idealized Japanese woman", or "the epitome of pure, feminine beauty".
Miyuki's beauty has been emphasized and acknowledged by most of the characters in the series, both male and female, as unmatched. Even Tatsuya, who is her brother, cannot help but be enthralled by her, despite his limited emotions. It could be said that because she is the only person towards whom he still has natural affection, he is still susceptible to her. The only character that has ever been mentioned as having beauty rivaling Miyuki's is Lina.
Miyuki has a slight mischievous side to her. She teases Mikihiko and Mizuki about the way they talk with each other in the middle of the war zone during the Scorched Halloween event. She once acted over-affectionately with her brother in order to mess with Mizuki, Erika, and Leo (It apparently had a great effect on Mizuki as she became completely lost in her dream world).  However, she has been constantly revealed to harbor forbidden feelings for Tatsuya, even lamenting once on the fact that she was born as his little sister, clearly indicating that she wishes to have a romantic relationship with him.
The thought of marrying another boy repulses and disgusts Miyuki. It is not a biological issue, so something like dancing was still acceptable. However, in Miyuki’s heart, the only one who was allowed to touch her is Tatsuya. The only one who could do as he wished with her was Tatsuya himself alone. Her love for her brother comes to such an extent that she is willing to offer her heart and body to Tatsuya. For her, "no matter if it was her body or heart, everything that she has belonged to Onii-sama."
As a candidate, and from Volume 16 and on as the future head of the Yotsuba clan, she is used to and is even displeased with flattery and compliments since many of these are coated with a mix of jealousy, envy, and malicious intent. However, she is always filled with bliss when Tatsuya compliments her.
Miyuki is extremely sensitive when it comes to her brother's whereabouts. She strongly dislikes the fact that people do not see her brother's real worth and states it occasionally, but she is often brushed off as being biased.  She also feels very guilty and laments the fact that she is the reason her brother has been 'chained'. Thus, she becomes careful to ask anything of Yotsuba to prevent the clan from asking Tatsuya to pay the favor or prevent them from restricting Tatsuya's freedom.
Miyuki gains great pleasure in meticulously taking care of Tatsuya. In place of her brother, it is Miyuki who gets angry whenever people look down on Tatsuya. She also gets irked and jealous several times when girls crowd around Tatsuya, mostly due to her own feelings for him. While she can control her actions at times like this, she unintentionally reduces the temperature around her due to her inability to control her magic when she's agitated. It isn't limited to her jealousy but instead whenever she has strong emotions (when she tries to calm down in order to not "go causing a frost on the beach in Okinawa in the middle of summer"). 
Like Tatsuya, it seems Miyuki puts him as the center of her world and always put him before herself in any matter. Likewise, because Miyuki is afraid one day they will have to be separated due to various reasons and just like how normal sibling would be parted once they are grown up, she intentionally put on an act in front of her brother by not being overly smart, not showing her real maturity, letting Tatsuya thinks her as a good girl, a soft and unreliable sister, so that he never think of the line "My sister doesn't need me anymore...". This is the notion that shows how much she feels about the results of the operation conducted by her mother that caused Tatsuya to own her as his only source of emotions and her own feelings towards Tatsuya. She wants her brother to stay with her for as long as they can, that she does not care even if others have seen her as a undependable sister. All in all, Miyuki actually has a facade that sometimes disguised her true personalities and opinions on every matter in the series, especially when in the presence of her brother. Ever since Tatsuya saved Miyuki from dying after being shot in Okinawa, she has devoted her life to him. As a result, her personality, everything that she does/has done, how she acts/thinks, how she interacts with others, what she is involved in or what her personality is like, etc. is because of Tatsuya. In short, everything involving/revolving around her, good or bad, is because of her feelings for Tatsuya.
Miyuki is the daughter of Shiba Tatsurou and the late Shiba Miya and is eleven months younger than her only elder brother, Tatsuya (her birthday falls on March 25, a month before Tatsuya's birthday). They are mostly mistaken as twins for being in the same year. Prior to the timeline, before the beginning of the series, their father remarried six months after their mother's death, and the two of them are living alone in a house, which is described as a place that vastly exceeds the average size. The siblings lived alone at first, however, later on Minami joins them as Miyuki's second guardian. 
Miyuki, The Masterpiece of Yotsuba
It is revealed that she is a modified-based magician (akin to Sakura Series) which is made especially for Tatsuya to have a life partner, and so that he would not go berserk and destroy the world. According to Maya, much technology was used in her modification, making Miyuki an extremely unique magician. Due to the modification done on her, Miyuki is a unique magician in an entire class of her own and even the Yotsuba will be unable to create another one like her. Compared to Minoru, who also has received similar modification done by Kudou Makoto before birth, Miyuki is a far more perfect and successful product proved by her stable health and lifespan. Because both of them are somehow similar in the aspect of their makings, this is actually the reason why they both have distinctive similarities; formidable magic abilities and striking ethereal-otherworldly physical appearances. 
- Miyuki is a descendant of the Yotsuba Family and was born with superior and formidable magical abilities. Due to this, she grew up as a pampered child and was raised in a manner befitting one of the candidates to succeed the family's Head position sometime in the future. Like other descendants of prestigious families, she attends the various type of classes with special tutors such as arts and more.
- Unlike her brother, who was technically demoted from an heir to being a mere servant, Miyuki enjoyed the privileges a Yotsuba deserves. She is now the number one potential successor.
- In Volume 8 of the light novel series, it is stated how unequally she and Tatsuya were treated by their family and relatives. The Reminiscence Chapter also showed how vastly different Miyuki's opinions and actions towards her brother were three years before the current timeline.
- Main Article: Okinawa Defense Navel Battle
- When the Great Asian Union attacked Okinawa in 2092, Miyuki — along with her mother Miya and her mother's guardian, Honami — took refuge in the army's shelter but due to some conflict with the Left-Bloods, were caught in a dire situation. Under the effects of Cast Jamming, they couldn't defend themselves; however, when the Psion waves weakened, Miyuki activated Cocytus and froze the enemy holding the jamming device.
- As a result, they were shot by the man's other companions. Lying in a state of near death, Miyuki was then saved by Tatsuya who used his innate ability Regrowth for the first time on another person. After this incident, Miyuki changed her front attitude towards her brother and was shocked when she learned about Tatsuya's emotions.
Miyuki is very intelligent, earning top grades on her assignments/homework, exams, classes, etc. In addition, she is very talented with various kinds of magic being part of the Yotsuba.
Like Tatsuya, Miyuki also received martial arts training from Kokonoe Yakumo, albeit to a lesser degree. While Miyuki is by no means a physical combatant, she remains in excellent shape and has far more physical strength than she appears to have.
Again, like Tatsuya, Miyuki boasts a tremendous Psion count and has great magical endurance. Unlike Tatsuya, however, Miyuki excels in all forms of standard modern magic, having great magical power, interference strength, and invocation speed. In fact, even as a first year, her magic power is said to be so great that no student at First High School (both in her year and the year above) competing against her could match it, to the point that both Mayumi and Mari find it is difficult to believe that someone in the same age bracket as her (which refers to Lina) could stand up to her Magic Power. Furthermore, Miyuki boasts tremendous magic power that she can easily pull off the magic of highest levels proving she is a formidable magician indeed.
As her magic abilities revealed bit by bit later in the series, it seems that Miyuki possesses the traits of the first Yotsuba lineage; a mind manipulation ability that was strengthened or unique.
Miyuki has the ability to detect the state of Eidos, or "information," through touch and smell. Not much is known about the extent of her sensory abilities, but she is able to use her senses to "smell" that Tatsuya had been in a fight with over 10 people and was injured in that fight. She also later, used her touch to receive the information from Tatsuya which he captures by his special eyes, in order to let her become informed of the whereabouts of enemies before using her magic to render their weapons useless.
|“||Just as Tatsuya could use sight to capture "information", so too could Miyuki detect "information" through touch. However, Miyuki was more capable than that, as she could also use smell to receive knowledge that was practically instinct.||”|
—Tatsuya on Miyuki's sensory abilities, Volume 11, Chapter 14
While Miyuki is very talented at magic, her specialty is Freezing magic, which slow downs vibrations, her magic is suited for large scale magic over a wide area. It is hinted that this tendency is a manifestation of her sui generis innate magic, Mental Interference Magic Cocytus. She is a skilled magician, and while she does not specialize in precision targeting, she is still able to accurately snipe 16 targets at once and can pick out target among many or vast range easily.
- Inferno is a Medium-Scale Oscillation-Type Magic. A magic which reverses the heat energy within a set area. Areas of bitter cold and scorching heat occur in adjacent regions. By dividing the target area into two sections and decreasing the kinetic and rotational energy of all objects within one section, this surplus energy could be released into the other section in the form of heat. This way, conservation of energy is still maintained while applying the principle of reverse entropy from thermodynamics. It is mentioned that this spell is used in the examination to become a Rank A Magicians.
- Niflheim is a Wide-Area Deceleration-Attribute Oscillation-Type Magic and considered a Rank A Freezing Magic that is able to produce dry ice and even liquid nitrogen from the air. This technique ignores heat and appearance, using magic to uniformly cool down all the objects within a set area.
- Freeze Flame is a Wide-Area Deceleration-Attribute Oscillation-Type Magic that freezes fire. It is a conceptual magic that prevented anything from burning. This magic can suppress the temperature of targets within a certain threshold. Against this spell, most firearms become useless as it becomes impossible to ignite gunpowder and fire projectiles.
- Miyuki's Counter Magic. It is used solely to shut down all magic with the exception of your own. Miyuki's Zone Interference is one of the best in the world and is so powerful that even Tatsuya and Lina have troubles under it.
This is Miyuki's true magic specialty and the category of magic that covers her innate ability: Mental Interference Magic. Outer-Systematic Magic does not manipulate the Eidos to produce phenomenon like Systematic Magic nor does it manipulate Psions like Non-Systematic Magic, but it manipulates the spirits themselves. This means Miyuki can manipulate the spirits and minds but the extent is still unknown since the details of this innate magic of her still not covered in the series - thus, it is still unknown whether she can alter the spirits' composition directly or just affect their state like freeze, or else.
In the Yotsuba family, each individual possessed a unique inherited ability which varied into two types. For some, they would have calculation area that was warped by a strong power, produce strong and unique/specialized magics for them (i.e. Kuroba Ayako's Perfect Diffusion, Tatsuya's Decomposition). For others, they would have some form of Mental Interference Magic ability unique to them that could not be classified within Systematic Magic. For examples, Miya, Miyuki's mother, possessed an Outer-Systematic Magic called Mental Design Interference, and Fumiya has Direct Pain.
However, in Miyuki's case, she possesses both traits; a strong and unique/specialized Mental Interference Magic ability.
- Cocytus is Miyuki's innate unique magic. Unlike her other Freezing Magic spells, Cocytus doesn't affect physical temperature. Instead, it freezes the mind and spirit. Miyuki is skilled enough with this magic to selectively choose whose minds to freeze even if the target is among a closely-packed people. However, because she serves as Tatsuya's magic limiter, this very unique and powerful ability becomes more available to her when she removes the seal to Tatsuya's magic power. During the events of the Master Clans Conference, it is revealed that Miyuki almost uses Cocytus while maintaining the seal.
- Mental Interference Magic - Magic Limiter - Pledge
- Miyuki is able to seal away a large portion of another person's power. Under Maya's orders, Miyuki uses this ability to seal most of Tatsuya's power, including his Material Burst spell. This costs her half her Magic Calculation Area and her impeccable control of her magic power. This loss of control causes her to subconsciously freeze her surroundings when she loses control of her emotions.
- It is later revealed that at the cost of all her Magic Calculation Area, Miyuki can seal away Tatsuya's Elemental Sight. It has been implied that once Miyuki places this particular seal because she no longer has any space in her magic processor, she is unable to use the magic to undo the seal or any other magic.
Nine-Schools Competition - 1st Year (AD 2095)
Miyuki is selected as one of the athletes for their school's team and participates the competition in two events for Newcomer Division. She is known by many people as the Ace of First High School's freshmen team and become popular quickly for various reasons during the competition.
She was initially registered for the Newcomers' Mirage Bat competition. But due to an accident befalling Mari, she was moved to the Official Division. In the Official Division, she used the Flying-Type Specialized CAD that her brother made recently as Taurus Silver and claimed the First Place in the match by a large margin.
Ice Pillar Break
Miyuki participated in the Newcomer's Division and won the first place after a magnificent match against Kitayama Shizuku, displaying a high level of magic skills.
- Shiba Miyuki was probably based on the Hindu goddess Parvati, with whom she shares many similarities and parallels to. Parvati is often hailed as the most beautiful of all the goddesses and the most powerful; she was also extremely devoted to her husband, Shiva, and is his great love and the main reason for getting involved in earthly affairs despite his general indifference to everything. Moreover, Parvati's name in Chinese (雪山神女) and one of her names in Japanese (雪冰天女) bear the "snow" (雪) character and roughly translate into "Snow Mountain Goddess" and "Celestial Snow Maiden" respectively.
- Some of Miyuki's spells (such as Inferno, Niflheim, and Cocytus) are named after a certain place or aspect of the underworld or afterlife.
- The kanji of "Miyuki" means "deep snow".
- True to her name, most of the spells Miyuki has displayed so far in the series are related to ice and/or freezing.
- Miyuki appears as a cameo in Durarara!! series. She appears as a painting in the side of Kyohei Kadota's van. After the door is broken by Shizuo Heiwajima during Saika arc, since then, Miyuki always appears in Durarara!! manga and anime series.
- An image of Tatsuya and Miyuki can be found in the ending credits of season 1 episode 24 of Accel World's anime, a poster advertising the manga appears episode 6.
- Despite critics who have reviewed the light novels, manga spinoff and adaptations praising the character, some of the fans have initially complained about her generic character designs despite the number of exaggerated adjectives the author used to describe her beauty throughout the series.
- In a character popularity poll held on the official anime website of Mahouka, Miyuki was voted by fans as the 2nd most popular character in the series, just behind Tatsuya, amassing a total of 5,770 votes.