|“||I lost all of what you could call feelings of love. They weren't sealed, so they can't be released. They weren't broken, so they can't be fixed. That which is lost, cannot be recovered.||”|
—Tatsuya, Volume 5, Summer Break
Tatsuya is wary of his aunt's control over his life. Unlike others, he is unafraid and unsubmissive towards her and is capable of holding a casual conversation with her. In Volume 14, it is revealed that in his contract with his Aunt, Miyuki's safety is the highest priority, with the duties with the Independent Magic-Equipped Battalion being second priority, and his Aunt's command authority comes in third after that.
Tatsuya admits that his abilities would triumph over his aunt's. However, he chooses not to defeat her because he is aware that doing so before a successor is named would result in a large power-struggle among the Yotsuba Clan, which may end up with someone worse taking over.
Until Volume 16, Tatsuya and Maya have a very business-like relationship, and he shows great reluctance in asking for help. At the end of Volume 16, Maya made the announcement that Tatsuya is her son and created a permanent place for (bind) him in Yotsuba, by announcing him as a Fiancée to the Next Head of Yotsuba Family.
Their relationship is cold and always formal, that of a master and servant. She reminds Miyuki to not look at him as a brother, because relying on him can hurt her future position in the Yotsuba Clan. Miya – as the rest of the clan – does not consider him as Yotsuba because he is not capable of freely altering the Information Bodies as a true magician should. He had to be turned by his own mother into a Guardian to have a place in the clan at all.
She explained this to Miyuki in Volume 8. She also told that he was subjected to her Mental Design Interference magic in his childhood. It happened when they were trying to create an artificial magician by implanting an artificial Magic Calculation Area into his mind. The operation was successful and he became capable of using magic, although to only a limited degree, but it cost him all his strong emotions and urges except one, sibling love. She describes their lack of parent-child attachment and parental affection trivial. Miya considers saving her life, after the incident in the shelter during the Okinawa Defense Navel Battle, to be his kindness towards Miyuki for not wanting her to feel sadness over losing her mother.
However, despite the unemotional explanation of the facts and events regarding Tatsuya's state, Miyuki faintly felt Miya suffering that she could not love her son.
Also in Volume 16 Maya told Tatsuya that the true purpose of this experiment was to take away his strong emotions for his benefit so that he doesn't have any emotional outbursts (Which may lead to destruction of whole world) and that Miya was reluctant to do the operation until the very end.
Maya also told Tatsuya in volume 16 that although Miya wasn't able to love Tatsuya, she did try her best to love him.
The two share a close relationship that is a bit more than a simple "master and student", and closer to family-like. Yakumo is usually one of Tatsuya's top sources of information, as well as a teacher for Magic Martial Arts and for any specially requested training, such as helping Miyuki prepare for the "Mirage Bat" event. He is the Shiba siblings' martial-art teacher.
For some reasons, Yakumo can't teach a new magic. But when Tatsuya ask for magic related advise, he often hints what to do, by using a related magic or a process, during their sparring matches.
|“||To me, the only thing I can feel is truly precious is you alone, Miyuki.||”|
— Shiba Tatsuya to Shiba Miyuki, Volume 8, Chapter 14
The relationship of Tatsuya and Miyuki is one of the focal points in the story of Mahouka Koukou no Rettousei.
Tatsuya and Miyuki do not act as normal siblings should, and instead, act more like lovers. Erika commented that they (Tatsuya and Miyuki) treat each other beyond that of a loving couple. The way Tatsuya and Miyuki act around each other in public causes various commotions and reactions among their peers, from embarrassment to discomfort to exasperation.
Due to the experiment conducted on him as a child by his aunt and mother, Tatsuya's strong emotions have disappeared, except for the familial love that he has for his little sister, Miyuki. Miyuki is the only person who Tatsuya naturally loves and his love for her is his only remaining strong emotion. He views himself as a tool designed specifically to guard Miyuki and considers it a privilege and an honor to be her Guardian.
Tatsuya constantly spoils Miyuki, going along with her whims as much as possible and is willing to spend a bulk of his finances just to make his sister happy. Their interactions can be called easy-going and comfortable for Tatsuya since he can constantly show his hidden witty and mischievous side towards his dear little sister, albeit only when they are alone.
Tatsuya is rather extreme and aggressive when it comes to protecting Miyuki. Tatsuya is willing to kill anyone who dares to cause Miyuki harm and he is willing to get into trouble just to protect her. Tatsuya would destroy anything that would cause Miyuki harm indiscriminately, immediate or otherwise. To be precise, the only fuel to his wrath would be anything that threatens her.
Still, Tatsuya acknowledges Miyuki's prowess and skill in magic and is willing to bring her along to the battlefield if she chooses so.
Tatsuya has been rendered speechless by Miyuki's beauty and he constantly comments and compliments the beauty of his sister, much to Miyuki's delight and embarrassment. Even after living with her for years, he still caught off his guard against Miyuki's beauty and often mesmerized by her.
He is the only person who can calm Miyuki down when she is distressed.
Tatsuya is ruthless when Miyuki is threatened. When Miyuki was on the verge of death during the Okinawa Invasion he went on a ruthless rampage soon afterwards to avenge her, murdering many and also leading to his first time using Material Burst.
In Volume 16, after Maya announced Miyuki as her heir, she also announced the engagement of Tatsuya and Miyuki; this made Tatsuya Miyuki's fiancé. After the announcement, once they were alone, Miyuki finally exposed her heart to Tatsuya and cofessed her love. Tatsuya was initially surprised. When Miyuki said the words "I love you", they resonated profoundly within him, causing an unknown sensation in response. Tatsuya quickly assured Miyuki that he would not push her away and that he did not consider her as someone abnormal or disgusting. He accepted her feelings and assured her that he will stay by her side till death. Tatsuya then told Miyuki that, currently, he only sees her as his little sister, but would try his best to love her as a woman, much to Miyuki's satisfaction.
In Volume 18, Tatsuya is still viewing Miyuki as his younger sister. He still does not yet have romantic feelings for her. Even if he had decided about how to respond to Miyuki's love, his heart hasn't reached that place yet. When Tatsuya came back after sharing the umbrella with Mayumi, Miyuki smells woman fragrance on Tatsuya's suit, she was extremely jealous, but she didn't show it because she feared that Tatsuya would hate her and cancel the engagement. After school, Tatsuya visited her class, Miyuki greeted him excitedly thinking he came to see her, Tatsuya tells her that he is only there to talk to Masaki, Miyuki feels disappointed as nothing has changed in regards to their relationship. On Valentine day, Tatsuya received a lot of chocolate. After he returned home, Miyuki has recently baked a chocolate cake for him. Miyuki questioned him about the bag she has seen Tatsuya carrying. Tatsuya said she doesn't need to worry as he did not received any Valentine's chocolate from Mayumi. Miyuki feels relieved.
Tatsuya's peculiar over-protectiveness and over-attachment to Miyuki are displayed once again during the pursuit of Gu Jie. Tatsuya needed to use his Elemental Sight at full power but he wasn't able to do so easily. Once at home, Tatsuya asked Miyuki to take a bath and come down to his lab late at night in either her night gown or a swimsuit. Miyuki complied and once at the lab Tatsuya revealed that he couldn't use ES at full power unless he removed the half of it dedicated to observe her at all times, and he did not feel at ease at all about doing so even though Miyuki was physically present in front of him. Miyuki reassured him that she was here and safe with him and that he shouldn't worry about that. Tatsuya acknowledged that but still felt uncomfortable. He said that he felt he would go crazy if he removed the ES on Miyuki. Therefore he asked her to help him calm down and held her in his lap while he tracked down his target.
Mayumi is the first person that Tatsuya meets in high school. Her cheerful nature and playful habits have caused much concern for Tatsuya, and is thus one of the characters he's very wary of. Still, Tatsuya acknowledges Mayumi's beauty and talent while she, in turn, holds him in high regards, admiring his skills and knowledge over CADs and Magic Theory.
While they are shown to share a friendly relationship with each other, Mayumi also has a romantic interest in Tatsuya. Evidence of this can be found in their interactions throughout the light novel and Mayumi's flustered behavior whenever Tatsuya casually praises her or whenever Tatsuya is mentioned to her by some others. Mayumi was still in self-denial at start but after sometime she became aware of her feelings but she's still not sure whether to accept them and proceed or to halt them.
In addition, during the events of Volume 13, Tatsuya and Mayumi met in a Fashion Center, where by chance Tatsuya happened to see Mayumi in her swimsuit. Mayumi appeared to be calmed at first, but she screamed when receding back to the changing room. After the incident, Mayumi and her twins sisters joined the Shiba siblings at a cafe, where she apologized to Tatsuya for making a fuss. She was shown to be quite disturbed when Kasumi said that the Shiba siblings were on a date. She fails to object to Tatsuya paying for the entire cafe bill.
After the death of Nakura, she was worried about asking Tatsuya for help, instead of Juumonji Katsuto. Due to Mayumi's strange focus on Tatsuya's circumstances, Mari voiced her suspicion that Mayumi is in love with Tatsuya. Mayumi weakly and unconvincingly objected the facts. It may be hint that she likes Tatsuya due to the loss of her confidence in her speech.
In Volume 15, in the hotel at Kyoto, Mayumi invited Tatsuya to have a meal together. After dinner, they went to the bar and Mayumi told Tatsuya to join her dating game by calling her Mayumi instead of calls her senpai however Tatsuya outplayed her by pretending to be her bodyguard and he addressed her as Mayumi ojou-sama. After Mayumi got drunk, they leave the bar and Tatsuya delivered her safely to her room. In the front of her room, Mayumi tried to put the key in her chest but Tatsuya snatched it immediately.
In her room, Mayumi asked Tatsuya to help her undress which gave Tatsuya a headache. Tatsuya stripped her quickly before anything else can happen and shoved her into the bed leaving her in her underwear. He went out of the room without a second glance back at her. In the afternoon, Mayumi asked Tatsuya why she wore only underwear in the bed, Tatsuya lied to her by saying that she stripped herself when she got drunk, Mayumi then dropped the bomb, she said she remembered everything, that Tatsuya should not have shoved her too roughly and her cheeks became red when their eyes met. At the National Magic High School Thesis Competition, Mayumi told Tatsuya that she will forget what happened that night in front of Tatsuya and Miyuki, this made Miyuki jealous and as a result she interrogated Tatsuya about what happened between him and Mayumi.
In Volume 17, Kouichi explained to his daughters that Tatsuya and Miyuki are from the Yotsuba Clan, he noticed the strangely shocked behavior of Mayumi after she learned about it. Kouichi also told them that Tatsuya and Miyuki are engaged and then he proceeded to ask Mayumi what she thought of Tatsuya as someone of the opposite sex, Mayumi blushed when she answered the question. Mayumi basically declined by saying it's inappropriate for the women's side to make the proposal, especially when Mayumi's the older one.
At the dining room of the University, Mayumi had a talk with Mari. In their conversation, Mari pointed out to Mayumi that she may have romantic feelings for Tatsuya, Mayumi only partly accepted Mari's words. But she admitted that there is nothing she can do, as she does not yet understand her feelings and it's inappropriate to make a move on an engaged man. Mari suggested Mayumi to object to her father's plan. Mayumi said she already did, but her father stubbornly encouraged her to marry to Tatsuya. Mari told Mayumi maybe the sly old fox had seen through her facade as Mayumi's still not wholeheartedly disagrees with the plan, then she advised Mayumi to thinking carefully and make the decision before it's too late.Later, in Volume 18, Tatsuya had a meeting with Mayumi and Katsuto, Tatsuya sat beside Mayumi, which reminded him of Mari's words, he thought he would be lying if he said he wasn't conscious of Mayumi as a woman, but his current emotions aren't capable for anything more than that. He knew about Miyuki's feelings and he accepted to be her fiance, but he doesn't have any romantic feelings for her except sibling love. To him, Miyuki is still his sister. Therefore, he feels obliged when Mayumi is still acting indifferent toward him, he decided to postpone thinking about Mayumi more in depth because it will hinder the work at hand. After the meeting Tatsuya escorted Mayumi to her car at Katsuto's request, and since it was snowing, Tatsuya shared an umbrella with Mayumi until she reached her transportation.
|“||This may be an underhanded way of speaking, but, I do like you. However, that's only as a friend. No matter how hard you try, I will never be able to think of you as a special woman. That will definitely be something painful for you — something that will hurt you." Saying so, a powerless smile drifted across his face. "Which is why I cannot answer your feelings.||”|
— Tatsuya to Honoka, Volume 5, Summer Break
Honoka harbors romantic feelings towards Tatsuya, and she has even confessed to him. After hearing Tatsuya's circumstances as he cannot reject or answer her feelings, Honoka said she will still like him until the day there is someone else that she can like.
Despite this, he gave her a pair of crystal accessories as Valentine's presents (which were chosen by Miyuki, he let her believe he chose them though).
In Volume 10, these feelings are proven to be quite strong, as the Parasite inside Pixie has absorbed these emotions and has since then dedicated itself to serving Tatsuya.
In Volume 17, Shizuku tells her about Tatsuya and Miyuki’s engagement. Honoka initially thinks that this is a joke, but Shizuku had a very serious and stiff expression. Honoka realizing that Shizuku is serious, she gets out of her chair and runs. She is then stopped by Shizuku and Shizuku struggles to contain her, causing her to lose her balance and she falls to the ground. Honoka apologizes and both of them goes to Honoka’s room. She begins to cry after asking Shizuku again if it’s true. She goes on to say Tatsuya said they were siblings and that Miyuki considers her as a friend. Shizuku’s tells her even though Miyuki’s feelings are different, Tatsuya only views Miyuki as a sister. Therefore Honoka still has a chance.
Shizuku goes on to say that nothing is set in stone and this will also be a surprise to the siblings. She mentions that Honoka has an option of becoming Tatsuya’s lover. However this is not now, nor when Miyuki becomes the head of the Yotsuba Clan, but when Miyuki and Tatsuya are married.
Shizuku asks Honoka if she is willing to give up on Tatsuya, Honoka replies that she isn’t. Honoka knows that Tatsuya has exceptional magic, and the Yotsuba will want him to leave behind a descendant. The road for Honoka is now difficult. She is not willing to give up on Tatsuya; however, she doesn’t want to snatch away her friend's (Miyuki’s) happiness. A little while later, Honoka goes into the arms of Shizuku in bed.
In Volume 18, on Valentine day Honoka called Tatsuya to give him her Valentine chocolate gift. Honoka wants Tatsuya to accept her gift, he doesn't refuse. He thanked her, but he reminded her that she doesn't need to give him any gifts as he is already engaged to Miyuki.
Honoka told him she doesn't mind, although Tatsuya was reluctant to accept her gift.
Erika is one of the close friends of the Shiba siblings. Because of her carefree and optimistic personality, she is someone who Tatsuya can easily talk with. Sometimes, Tatsuya reveals his evil nature when he teases Erika. He is also one of many people who witnessed most of Erika's embarrassing moments.
In Volume 1, when Erika was surrounded by multiple club employers, Tatsuya thinks it was because she is a beauty, just a different type of beauty compared to Miyuki. Furthermore, Tatsuya was impressed by Erika's physical abilities and later acknowledged her observational skills.
In Volume 3, Tatsuya was chosen as a competitor and he felt depressed on the stage because of the negative atmosphere and pressure from the audience, Erika bravely lead her class through Bloom row to cheer for Tatsuya, which made him feel better. When Tatsuya, Miyuki, and Mizuki witnessed Erika's talk with her brother, to not let her feel down Tatsuya agreed to treat her something. After that, they all came to his room to have lunch, Tatsuya felt embarrassed for Erika buried her head into his pillow.
In volume 10, Tatsuya directly cheered up Erika by promising that he will not hold back with Lina next time (if she is truly guilty) and indirectly cheered up Erika the second time, when she avoided meeting him, by having Mikihito bring a sandwich to her (and Mizuki).
In the Visitor Arc, Tatsuya tried to dissuade Erika from continuing when she was starting to get close to the truth about his relationship with the Yotsuba family. However, when she was about to ask, he yelled at her, silencing her not with his tone or volume, but with his intent. He told her that she shouldn't go any further than that, or it would make things awkward for everyone, which she agreed.
In Volume 17, when Tatsuya's identity was finally revealed, she is one of the few classmates who still treats him normally. She scolds Mikihiko and convinces Mizuki to not be scared of Tatsuya. In chapter 5, when Hirakawa Chiaki throws sarcastic comments about Tatsuya, Erika confronts her and when Chiaki tells her that she defends Tatsuya because she likes him, then Erika tells her that she is not stupid enough to become rivals with Miyuki and does not want love while putting her life on the line.
Tatsuya feels sympathy for Lina, as he believes that she is not suited for military work. Tatsuya believes the best thing for Lina is to leave the STARS and become a Japanese citizen. He also empathizes with the burden she must uphold as a Strategic-Class Magician. Despite her attempts to capture and defeat him in battle, Tatsuya still considers her a friend and is willing to help her out in any way.
Tatsuya praises her skill, intelligence and her beauty that has left him speechless. Lina also acknowledges Tatsuya's skills and intelligence, but she is also a little bitter about it, because she's very prideful and doesn't believe someone to be more skilled and powerful than herself. Lina does hold feelings for Tatsuya, but is shown to be too stubborn to admit them. It is also implied in the epilogue, for Volume 11, that Miyuki considers her a rival, not just in magic, but in romance as well.
In volume 17, Lina acknowledged Tatsuya's engagement to Miyuki and congratulated him. As a son of the Yotsuba clan leader, Lina tells him to be careful because right now he might be targeted by terrorists.
In volume 17, Mari emails Tatsuya for a private meeting after she meets with Mayumi. During the meeting, she asks Tatsuya what he thinks about Mayumi. Tatsuya answers without much thought that she is a talented magician and exceptional person. Mari does not like the response and asks again what he thinks about her as someone of the opposite sex; to which Tatsuya responds that she is a lovely person. Mari presses again that this is not what she meant; Tatsuya wonders out loud if she is referring to a kind of sexual attraction, which causes Mari to blush.
Mari explains that there are intentions to match Mayumi with Tatsuya; similar to the situation with Ichijou trying to force a commitment with Miyuki and Masaki. Mari says Mayumi has no clue what her true feelings are towards him and asks Tatsuya if he would consider marrying Mayumi. Tatsuya finally understands the situation and says he has no intention of breaking his promise to Miyuki. Tatsuya ends the conversation and pays the bill before leaving.
Miya Yotsuba's guardian. He had a good relationship with Honami as she treated him as a son. During the Battle of Okinawa, Sakurai aids Tatsuya going as far as leaving her post as Miya's guardian (with Miya's permission) in order to defend Tatsuya from an incoming naval artillery bombardment. She sacrifices herself, dying from magic overuse to allow him to use Material Burst.
Juumonji and Tatsuya do not show anything more than a professional-like relationship. Juumonji respects Tatsuya's abilities and is one of the ones who supported the idea of his participation as CAD support during the Nine Schools Competition. Likewise, Tatsuya respects Juumonji's abilities and is impressed by the strong presence that Juumonji emits, although he remains wary of him as Phalanx and Decomposition are natural enemies.
Juumonji suggested that Tatsuya should integrate himself into the Ten Master Clans. He suggested Tatsuya do this by marrying Saegusa Mayumi or one of her twin sisters, after he defeated Ichijou Masaki. Juumonji warns that his victory over a member of the Ten Master Clans "is not to be taken lightly."
As the series progresses we see that Juumonji suspects Tatsuya is part of the Ten Master Clans. Juumonji is aware of the fact that Tatsuya is a member of the military with the rank of 'Special Officer' due to the Yokohama incident.
Kazama is Tatsuya's commanding officer. There is a definite respect between them due to their both being disciples of the same master, but should the situation demand it, both will desert the other without a second thought.
The two appear to share a friendly professional relationship. Kyouko taught Tatsuya how to hack and manipulate information systems. She has been his support during official and unofficial operations. She treats Tatsuya like a younger brother whenever the two meet outside of work, and also tries to tease or flirt with him, despite his stoic nature.
Tatsuya has also helped Kyouko personally. She asked him to "inspect" Kudou Minoru for her to discover the reasons of his poor constitution.
The cold attitude towards Tatsuya is the result of Tatsurou's desire to avoid provoking the main Yotsuba family and the other branches as well as to protect himself. The intelligence and skills of Tatsuya produce a fear that transcends jealousy and is close to the terror, which causes lunges at him.
On the other hand, Tatsuya is not interested in getting his father to treat him as a son and Tatsurou's jealousy and his attitude do not affect Tatsuya in the very least. Miyuki also mentioned that if Tatsuya weren't her guardian, he would be forced to work for Tatsurou at FLT.