|Spoiler Alert: This page contains spoilers. Read at your own risk.|
- 1 Appearance and Personality
- 2 Relationship with the Shiba Siblings
- 3 Abilities
- 4 Equipment
- 5 Gallery
- 6 Trivia
- 7 References
Appearance and Personality
Fumiya has a pair of large pupils within his almond shaped eyes with a finely shaped set of red lips beneath a straight, narrow nose which makes him look adorable. As a result, he often has to cross-dress during missions, which irks him greatly. Although he is already a high school student, there is still no sign that he is physically unable to continue pretending to be a girl, having not gone through puberty yet.
Born in June 2080, Fumiya is described as a cheerful, very serious young boy. Sometimes, he has difficulties handling his sister Ayako. Fumiya is someone who is open-minded and is only a handful of people who is able to understand that Tatsuya is more than just a regular guardian. He also admires and respects Tatsuya greatly, even overestimating him many times. This is just his pride and adoration of him since they are related by blood.
Relationship with the Shiba Siblings
Fumiya and Ayako are the closest in age to Tatsuya and Miyuki in their family, and among the few they knew who weren't enemies. They have a good relationship with the Shiba siblings since their childhood. They occasionally visits the Shiba siblings' residence for casual talk sessions and exchange important information.
One of the reasons Fumiya adores Tatsuya is because he taught Ayako her Perfect Diffusion spell that established her name, Kuroba Ayako, among the Yotsuba Magicians. At the same time, this became one of the reasons for the Kuroba twins to overestimate him.
Unlike the other members of the Yotsuba, he views Tatsuya as someone worthy of his respect and admiration. He calls him "Tatsuya-niisama", the highest form of respect given by siblings and is always happy to see him. He dislikes that his father views Tatsuya as only a mere guardian and tool, not as a member of the Yotsuba Family.
Double Seven Chapter
Fumiya and Ayako visits the Shiba Sibling's home for the first time and reports the activities of the Humanists they recently captured. Tatsuya commends Fumiya on his skills in utilizing the Kuroba's intelligence network causing Fumiya to get flustered and Ayako teases him for it. Tatsuya and Miyuki watches them argue, having thoughts that they are close siblings. After giving a more detailed report, Tatsuya wanted to tell them to stay over night since its already late but in the end chose not to do so. He wanted to go in First High to be with the Shiba siblings, but was ordered to enter Fourth High, as Maya thought it could possibly endanger the secret of Miyuki and Tatsuya.
In order to establish the fact that the twins and the Shiba siblings were complete strangers, they introduced themselves publicly, calling him "Shiba-senpai" and asked for guidance for engineering in order to set up an excuse to meet later.
Later that night, Fumiya and Ayako investigate the area of the Steeplechase Event, continuing their mission to investigate the parasite use in the competition. As they survey the area, Tatsuya calls out to them. Both were surprised by this then Fumiya greets him while Ayako is upset that Tatsuya scared her and they continue their discussion on how to proceed. After deciding not to proceed for now, Tatsuya tells them that the mission concerning the parasites will be handled by him and that they should concentrate on the Nine Schools Competition which is another mission from Maya for the Kuroba twins to draw attention to themselves. While their stance as a Kuroba magicians believe that this is an unacceptable request, but since it's Tatsuya they accept it. 
When Mitsugu's right arm got severed by Zhou Gongjin's Xiao Tian Quan (Howling Celestial Hound) Shadow Beast magic, Fumiya calls Tatsuya but Mitsugu refuses help from him. Tatsuya tells him that Fumiya and Ayako will be sad if he leaves him like this and restores his right hand with Regrowth while thinking that he is glad that he didn't bring Miyuki and Ayako with him. 
Ancient City Insurrection Chapter
Fumiya and Ayako visits the Shiba Sibling's home to deliver a letter from Maya which requests Tatsuya to aid the Kuroba in their hunting Zhou. Tatsuya confirms that to the Kuroba twins that they are aware of the letter's content since its a request Tatsuya can decline then Tatsuya accepts the request. Fumiya is ashamed of letting Zhou get away but Tatsuya consoles him then they talk about the recent escape of Zhou and being protected by "Traditionalist". After the Kuroba twins got back on their hotel, Fumiya is concerned about their other mission to be shadowed on their way back and that it might lead enemies to the Shiba Sibling's home but Ayako assures him that they'll have the enemy by the tail if they do. 
Yotsuba Succession Chapter
Mitsugu tells Tatsuya to not attend the New Year Family Gathering but will not do anything for the sake of Fumiya and Ayako's feelings for Tatsuya.  While having dinner with the other candidates at the Yotsuba Main House, Fumiya withdraws his claim as candidate for Head of the Yotsuba Clan and formally supports Miyuki. 
Fumiya and Ayako are members of a "research club" with Tatsuya. Tatsuya informs them of Tookami Ryousuke admits being part of FEHR and gives them the information on FAIR and the relics.  Fumiya visits the Shiba Sibling's home and informs them of FAIR's business-relationship Advancement of Humanity Front and their goal to a relic for FAIR at an excavation site and joins the pursuit of the Humanity Front members with Ayako. They captured over twenty members but not the leaders.  Fumiya and the Kuroba Family encircles the house of the Izayoi Family who is sheltering Kurenai Anzu while Tatsuya's group negotiates with them to hand her over peacefully. He pursues Kurenai and successfully captures her after Tatsuya dismantles her reflect magic. 
Fumiya has an inherently high sensitivity to pushions as well as psions because of having a high aptitude for Mental Interference magic. But is still inexperienced and has a way to go to master the skill of distinguishing those who are close by. 
Although modern magic places the emphasis on altering phenomena and so has a tendency to put off improving perception abilities, the Kuroba Family spends more time developing perception abilities than normal magicians as they are responsible for gathering intelligence for the Yotsuba Family. This tendency to focus on perception abilities is further shown by the fact the Kuroba family inherited a school of Ninjutsu, a type of Ancient Magic known to include a number of ancient information gathering techniques.
Additionally, Fumiya has been show to be able to track a person's residual trail in the Idea when they use magical and supernatural abilities. It is sufficient to allow him to pursue a target, without ever losing sight of their whereabouts despite losing line of sight literally.
As one of the candidates to being the Yotsuba heir, Fumiya is both skilled and powerful. In the Nine Schools Competition of 2096, in the Monolith Code event, he single-handedly took down First High School's team in the rookie division, a team that was undefeated prior to its match against Fourth High School's team and a team that included Shippou Takuma who was able to fight both Saegusa Kasumi and Saegusa Izumi at the same time to a standstill.
- Mock Teleportation (擬似瞬間移動)
- Mock Teleportation is, as the name suggests, a spell which allows the user to move almost instantly to any location within range via the creation of a vacuum tube. Fumiya is highly proficient at the spell Mock Teleportation, though that is by normal standards as compared to his sister Ayako he still has a long way to go. Because Ayako has the greater level of mastery, she is the one who will usually cast Mock Teleportation on their missions, but Fumiya can fully utilise the spell when operating solo.
- Fumiya has been shown to be able to use this magic to collect all the gas from a smoke bomb into a ball and then eject it from a room by means of a window.
- Diffusion (拡散)
- This is a spell which targets sound which Fumiya uses to move stealthily. By setting an area of effect, the magic expands to obstruct sound whilst not preventing the average noise from passing through. This allows one to move around whilst anyone nearby will only hear the background noise rather than silence which could tip them off. As such the magic is designed to be indistinguishable.
- This technique is also a strong point of his sister Ayako the same as Mock Teleportation and, although not to his sister’s degree of perfection, Fumiya's mastery of ‘Diffusion’ far exceeded the level of the general combat magician due to being in a position to observe his sister's mastery.
- Jump (跳躍)
- A simple spell to allow one to jump to superhuman heights. Fumiya uses this to launch himself into the air when the need arises, such as during the pursuit of a target.
- Self-Acceleration (自己加速)
- A spell to enhance one's own speed, Fumiya uses this to accelerate his movements when needed, such as during the pursuit of a target.
- Anti-Object Shield (対物シールド)
- A defensive spell, this technique allows Fumiya to erect a barrier around himself which causes objects entering it to lose kinetic energy and fall to the floor. The spell is powerful enough to stop both thrown weapons such a shuriken and knives, to projectiles such as the bolts from a crossbow.
- Air Blade (飛空刃 ひくうじん)
- This spell Fumiya uses is a variation of Air Bullet which fires a mass of thinly compressed air at high speed. It is a highly lethal spell able the literally shred a target and cut deeply into a human body.
- Hot Air Blade (熱風刃 ねっぷうじん)
- A similar spell to Air Blade, Hot Air Blade is a variant with a lower lethality as energy is used to heat the air whilst the spell is being compressed, which lowers the speed. However, due to the heat posing a fire risk, the spell's use can be restricted due to the environment where causing a fire is an issue.
Ancient Magic - Ninjutsu
The Kuroba Family inherited a school of Ninjutsu and as such it's operatives are trained in the techniques of this ancient school of magic.
- Shouinkyou (照陰鏡 しょういんきょう)
- Shouinkyou, meaning 'Mirror to Illuminate the Unseen', is based on Shoumakyou, meaning 'Taikoubou’s Mirror of Illumination' which discloses the self’s true colours. As ninja place the importance of escaping from an opponent rather than killing them, they developed this technique to ‘sense of the thirst for blood’ and it is bequeathed as a special technique. The ability allows Fumiya to sense the killing intent of people in range, allowing him to identify hostile people within the vicinity and track down potential targets by allowing him to sense their location from a distance, regardless of any physical barriers between then.
Among the living members of the Yotsuba family, he is one of the two (Other one is Tsukuba Yuuka) who has the highest abilities in mental interference magic. Although their skills were still inferior to their parents' generation, in terms of talent and potential, these two competed for 1st, 2nd place among the whole family.
- Direct Pain (ダイレクト・ペイン)
- This is Fumiya's innate ability and as with all innate ability, it can be used at a high speed even without a CAD. With this ability, Fumiya can directly "imprint" pain into another person's mind. Fumiya is able to control the level of pain his opponent experiences and can slip this ability in with another magic to fool his opponent about the source of his or her pain.
- Evil-Eye (凶眼)
- As an MI user, Fumiya is able to use a the spell Evil Eye, referred to as the 'True' Evil Eye. This spell is a magic to cause emotional attachment to feelings of avoidance in other parties by means of one’s gaze, to the point of inducing panic. At its greatest output, this magic that can drive people to suicide in a state of panic.
- Phantom Blow (幻衝)
- A flashy but intangible attack that can incapacitate the opponent by causing concussive-like symptoms using a single Psion shock wave.
Fumiya's CAD is a knuckle with a button by the index finger slot to activate his magic Direct Pain
Needle Gun Armament Device
When Fumiya is on a mission he is often required to hide his true abilities. On way he does this is by using a Needle Gun Armament Device which fires needles by means of movement magic and act as a medium for his spell Direct Pain to hide the fact he is using Mental Interference Magic.
Fumiya is proficient at knife combat and often uses a knife for close quarter fighting. Fumiya's proficiency is al a level where he can use knifes to fight with professional assassins in close quarter combat.
A gimmick his father added to Fumiya's equipment after reading about them in a Western novel, Fumiya's combat outfit includes flash grenades disguised as decorative buttons which he can rip off and throw to stun the enemy.
Cross Dressing Disguise
In order to protect his identity Fumiya is often forced to disguise himself as 'Yami', a young girl. This is possible due to his naturally feminine appearance. His disguise includes a number of defensive options, such as being made from bulletproof materials, allowing the clothing to double as a type of basic body armour.
- Ayako and Fumiya are the third pair of twins featured in the series, other than the twins Kasumi and Izumi, and Miya and Maya.
- Volume 8, Chapter 3
- Volume 8, Chapter 4
- Volume 12, Chapter 4
- Volume 12, Chapter 9
- Volume 13, Chapter 5
- Kuroba Twin's Story: Mission to Draw Attention, Chapter 2
- Volume 13, Chapter 8
- Volume 14, Chapter 1
- Volume 16, Chapter 2
- Volume 16, Chapter 6
- Magian Company Chapter II, Chapter 9
- Magian Company Chapter II, Chapter 11
- Magian Company Chapter II, Chapter 12
- Plan to Assassinate Tatsuya Shiba, Volume 1, Chapter 10
- Plan to Assassinate Tatsuya Shiba, Volume 1, Chapter 6
- Plan to Assassinate Tatsuya Shiba, Volume 1, Chapter 9
- Volume 13, Chapter 6
- Volume 12, Chapter 14
- Plan to Assassinate Tatsuya Shiba, Volume 1, Chapter 7
- Plan to Assassinate Tatsuya Shiba, Volume 1, Chapter 8
- Volume 22, Chapter 1