Manabu is her older brother as well as the student council president. Suzune looks up to him and strives to be noticed by him in a positive light. But because of her status as a student in D-class, she is seen by her elder sibling as nothing more than an embarrassment to him. Despite her respect for him, she holds some resentment towards him as she got irritated when Kiyotaka asked if they were related but Suzune's glare prevented him from broaching the subject further. However, this also could be because she doesn't want to answer any personal questions regarding her life and may not resent her brother.
While talking with him it was shown that he was very cold towards her, due to her position in the lowest class while she tried to nervously talk to him, in contrary to her composed and serious behavior. While saying it's not her fault for being placed in D-class, she stated she will reach A-class as he angrily grabbed her and listed all the shame she has brought to him and the family's name. He then demanded for her to leave the school while she is shown to be afraid, a first for her in the series. She tried to explain her plan of reaching A-class but he dismissed this as an excuse and attempted to assault her when Kiyotaka intervened for her sake.
After a brief skirmish between the two, Manabu voiced his surprise that Suzune had made a friend and derided her words after she said that it was not the case before leaving his shaken sister with advice to move up.
She was seen being nervous with his presence at the hearing for Ken and was unable to speak until Kiyotaka tickled her to regain her resolve. Despite her strong speech and determination during the case, Manabu was not impressed and continued to not expect anything more from her.
It is shown that, in spite of their turbulent relationship, Suzune keeps a portrait of herself and her brother in her room, showing that at one point they were close. During the summer outing, though they didn't interact personally, Manabu bore witness to Suzune's speech of how D-class will reach A-class. After the speech, his only reaction was a glare at his sister, who responded in the same way. It is unknown what he thinks of her now ーthough this happened only in the anime.
During the survival island test, Suzune revealed to Kiyotaka that one of her main reasons for aiming for A-class was so her brother would acknowledge her talents.
Suzune is the first person that Kiyotaka interacted with when entering the school. He first caught notice of her when they were on the bus after witnessing Kikyō trying to persuade Rokusuke to move from his seat for an elderly woman but to no avail.
They formally meet when she inquired as to why he was looking at her as he replied that he saw a similarity between them in the bus incident. She told him not to compare them as she chooses not to get involved in such trivial matters as Kiyotaka notes that she's "worse than he is". They are later shocked to learn they are classmates, which Suzune stated was a bad coincidence after they sat next to each other.
After a few days in class, they appear to get along since they are both loners who barely associated with their classmates. It was noted by Kikyō that Kiyotaka is the only person in the class that Suzune interacts with at all and tried asking him to help her befriend Suzune, but it failed. In response to his supposed conspiring, Suzune forced Kiyotaka to aid her in reaching A-class and though hesitant he complied after she put pressure on his choice.
Though she forced him to help her reach her goal, they appear quite close as he intervened when her brother was about to assault her. When she cried out for him to stop, he noted the sincerity of her voice which he never saw before in her, while she watched on in awe at him swiftly avoiding her brother's attacks. Manabu even stated he was surprised to see that she made a friend, but she bluntly replied that Kiyotaka was just a classmate of hers. After her brother hinted that Kiyotaka is more than he appears to be, she herself began to inquire about him only to receive vague answers, calling him strange. After a comment from him stating that her distant nature was what most likely caused her to be put in D-class, it made her ponder on the topic and whether she holds herself back.
After this event, she begins to become more aware of Kiyotaka's talents, as she immediately knew he helped the class pass their tests rather than Kikyō and questioned him over why but he didn't give her a clear answer.
While she merely sees him as means to enter A-class, she later asked him about his close association with Kikyō, noting he seemed more inclined to help her than anyone else. Her tone of voice hinted at some irritation with his time spent with Kikyō.
During the hearing for Ken, while Suzune found herself unable to speak out of fear from her brother's presence, Kiyotaka tickled her, which brought her back to her senses and she was able to give her case without problems.
She later has him aid her in her in the goal to save Ken and they are successful in forcing C-class to withdraw their complaint with both using impressive tactics to do so. Afterwards, she went to talk with Sae Chabashira, who said there was more to Kiyotaka that meets the eye, which caused Suzune to further wonder the true extent of his abilities and whether she could trust him. Suzune met him in the hall and the two would walk together in the rain where she accused him of manipulating her so she would force C-class to withdraw their complaint. This leads her to question him about his motives to assist in reaching A-class while simply receiving the response that she forced him to. She questioned him further about his past and whether she could trust him, with Kiyotaka replying he was simply looking out for a friend. She dismissed this as a lie, pushing him further to reveal his history. In response, he told her that he will help her reach her goal but told her to not inquire about his life, marking the first time he ever got somewhat aggressive towards her.
Despite the exchange, they were shown to still be on good terms as Kiyotaka invited her to the pool (which she refused at first) where he asked her to aid him in stopping the boys of their class from peeping on the girls during the summer break. When some of the girls discussed their associations with Kiyotaka, with Suzune stated she had no interest in whoever befriended him. Kiyotaka also tried to get her to loosen up by having her play with the students, though she still wondered why he hid his physical capabilities. Later on, she helped Kanji escape the girls changing room by giving a speech to distract everyone, which later let her go into the change rooms alone and messed up the boys' plan that Kiyotaka informed her of. She ended the day in good spirits after Kiyotaka pushed her into the pool, leading her to do the same in reply when everyone else there with them joined in.
Later that night, Kiyotaka sent Suzune an email which contained a picture of her with the other students, as she remarked on how she got along fine without others but smiled at the gesture anyway.
During the school survival test, Suzune asked Kiyotaka about his future after school but received no answer. After the panty-thief incident, the girls decided to move their side of the camp Yōsuke Hirata was chosen to guard the boys. Suzune had no problem with this but made sure that Kiyotaka was also chosen to guard because he didn't seem like the type to do anything scandalous. Her decision was met with some initial protest since Kiyotaka wasn't well known in the class but the decision was made regardless.
When he finished guarding, she approached him and he asked why she made him a guard, as Suzune replied that she didn't trust Yōsuke as he seemed like a secretive person with a different side to him. While she said the same went for Kiyotaka as well, her reason for making him a guard implied that she trusted Kiyotaka to a degree. Also, she blushed when he put his hand on her forehead after finding out she was sick and hiding it from the class. Suzune was left in shock after deducing Kiyotaka burned the survival manual, leaving her to wonder why he might've done so.
After the survival test, he found an unconscious Suzune after her fight with Ibuki and took her to a tree before she awoke. They talk, where she confided in him of her reasoning for wanting to reach A-class and admitted she did indeed want allies, before he implored her to withdraw from the test, but she refused out of pride though although she collapsed soon after, and Kiyotaka took her to the teachers and to be withdrawn from the test. After the test, she was surprised the class had won the survival test and immediately suspected he had a hand in it. She met up with him and questioned him on how the class passed the test and he told her his plan and how he outsmarted the other classes with various tactics, which left her in amazement at his intellect. She soon inquired about what motive drove him since he had no clear intention of reaching A-class. She was also surprised that he gave her credit for the correct guessing of the other class leaders, much to her dismay.
In the anime, she caught up to him again and confronted once more as he calmly stated she needed allies and noticed she finally changed. After he confirmed he did everything to help her, she got flustered and blushed before begrudgingly thanking him as she said she will see him as an ally. This displayed that she has come to respect him since he has helped her in both overcoming her social shortcomings and when she is unable to complete a task.
In the light novel, their relationship is more or less similar to the one in the anime as he tries to befriend her but is rejected due to her personality.
Because of her goal to be friends with everyone, Kikyō has tried to extend this to Suzune but has failed in the end due to the latter's disinterest in friendship. Kikyō once tried to enlist Kiyotaka since he was the only person that Suzune spoke to every day. Kikyō explained her plan was to meet with Suzune and become friends though Suzune saw right through it and rejected the offer once again.
Unknown to Suzune, Kikyō harbors great contempt for her cruel and antisocial ways, shown when Kiyotaka found her throwing a tantrum and cursing Suzune's name. However, she appeared to want to hide this revelation from others as shown when she threatened Kiyotaka to keep quiet about the incident.
It appeared that Suzune is somewhat aware of Kikyō's contempt for her, as while listing her observations on her classmates, she reflected on a look Kikyō once gave her and wondered why she would try to associate with her if she possesses hatred for her. Despite that, they are seen talking civilly, as they discussed the friendships that Kiyotaka has made with several girls and it seemed that Kikyō believes Suzune has affections for Kiyotaka while teasing her but Suzune shrugged it off. They are later seen playing in the pool splashing each other after Kiyotaka and Suzune threw each other in the pool.
During the survival island test, Kikyō acknowledged Suzune's talents and made her leader of D-Class as it would be unexpected from the other classes. Suzune was very surprised by Kikyō's request and followed through with the suggestion.
In the light novel, Kikyō assumed that Suzune knew about her dark past and hidden personality because both went to the same middle school, and Suzune planned to expose them, resulting in Kikyō using any means necessary (mostly by betraying D-Class) to have Suzune expelled before her own secrets are exposed.
The two a rocky standing due to Suzune's habit of speaking her mind and not being afraid to hurt people's feelings with blunt words, which only provokes Ken's short temper. She soon implored Kiyotaka to convince Ken to join her study group but he refused and went to basketball practice. Suzune was not done with him as she personally went down there and made him think about his athletic career and how it would be at stake if he were to be expelled, which persuaded him to go study. However, Suzune's blunt personality got the better of him and he voiced that he didn't join just to be insulted, but she remained unbothered.  When Kikyō gave everyone the old test exams to help everyone, they all got passing scores with the exception of Ken. Because he failed, Ken was set to be expelled from the school but was prevented by Suzune and Kiyotaka sacrificing 100 thousand points to get the point he needed to pass. The two later attended a celebration party at Kiyotaka's room which was attended by several other classmates. When Kikyō hinted that Kiyotaka helped Ken out, everyone stopped their activities and looked to see if this was true but Kiyotaka passed the credit to Suzune. A startled Suzune was barely able to explain to a curious Ken that she did it for her own benefit.
Later, Suzune helped him in a case to prove his innocence after he is accused of fighting three students. Initially, Suzune struggled to say anything (due to her brother's presence) but with help of Kiyotaka, she was able to speak on Ken's behalf. She began her speech with criticism of his character which angered him at first but she stated he was not at fault for this incident, to his shock. Ken watched as Suzune used her charismatic words to bring evidence that he was not at fault first by pointing out holes in C-Class's story and by bringing in Airi who had pictures of the incident. When those representing C-Class protested, Suzune stated she would not accept any compromises and wanted to dismiss the accusations towards Ken who sat staring in admiration of her abilities.
When C-Class withdrew their complaint against him Ken informed Kiyotaka of this (not knowing he aided in this act). Kiyotaka congratulated him on this and when the relieved Ken wondered Suzune did something to help him, Kiyotaka again gave her the credit. After the brief celebration, Ken called Suzune amazing for her actions before he left for practice as Kiyotaka looked on. 
They hung out with another during summer break and after Kiyotaka threw Suzune in the pool to get her to have fun. Ken and the others thinking they were playing a game, joined in and started splashing Suzune.
In Episode 8, it is hinted that despite their previous hostile interactions, Ken has developed romantic feelings for her due to his excitement after he was told her first name, repeatedly calling it cute.
Suzune is insulted that she was placed in a class full of the school's idiots. She does not try to get friendly nor associate with anyone except for Kiyotaka and is rather distant towards her other classmates, which has given them the impression of her being cold-hearted and uncaring. She also interacts well with Airi as she worked with her in stopping Ken's expulsion and thanked her for the help. Some of the class acknowledge Suzune's intelligence and many have tried to befriend her but her disdain for friendship causes her to keep them at arm's length.
During a confrontation with Mio, she acknowledged her previous condescending views of the class were wrong as she saw that she was no better than in having to resort to violence to settle things.
After the survival test, it turned out Kiyotaka has made it appear that she was the one responsible for D-class' victory in order to have others put their trust in her. As the class expressed their gratitude to Suzune, she was nervous and flustered by their attention as she tried to explain what really happened but to no avail.
Suzune didn't interact with Sae very much until Suzune offered to help Kiyotaka pay for stopping Ken's expulsion. Sae was amused by this and accepted their payment and told them not to disappoint her since they did something nobody in the history of D-class has done. It appeared after this she did indeed become interested in Suzune after she told her that she intends to ascend to A-class stating those with defects can overcome them and advance.
Following Ken's fight with C-class, Suzune later went to talk with her teacher after she called her up. Sae had inquired as to how Suzune had got the other class to withdraw their statement but was given no answer, in which Sae instead told her to understand Kiyotaka better since Suzune wanted to know the "defective" traits of those around her and his was that he hides his abilities. Sae's words led to Suzune having a talk with Kiyotaka about his past and why he chooses not to draw attention to himself.
While these two have barely interacted, during the survival test Suzune was impressed by Honami's way of leading her class. earlier than that however at the pool trip, during changing, Suzune questioned Honami over her chest size as the latter was somewhat embarrassed on answering. Suzune also agreed with Kikyō's comment of Honami being relatively close to Kiyotaka while Honami just smiled ーanime only. Like the others, Suzune appears to have studied Honami's personality and behaviour and described her as intelligent, talented and kind, which meant she recognized her capabilities.
These two had minimal interaction during Ken's hearing, where Suzune played a role in stopping his plans of getting him expelled. Later on, he spotted her giving a speech to everyone at the pool recalling her as the girl who foiled his plans.
They formally met on the school's cruise ship. Kakeru found Suzune sitting at the bar and addressed her by the first name, giving hints that he is aware of what she did to get the complaint withdrawn. Suzune, who seemed to be disgusted by his presence, found his arrogant attitude off-putting and told him to keep away from her but he responded by taking a picture of both her and Kiyotaka, claiming to be a fan of her and stating he had already made plans to take care of her personally, while telling her to look forward to it.
During the deserted island test, he was seen persistently flirting and making advances on Suzune, as she and Kiyotaka were scouting C-class, stating that he will prepare a special tent for the two of them, as well as, making her taste real heaven, where she glanced back at him presumably disgusted and freaked out. After that, she is seen leaving with Kiyotaka, stating that being there any longer than they should have will just make her even sicker.
Not much is known about their relationship, but they have a rivality relation going on.
In the survival island test, Suzune was seen reprimanding Mio for stealing the key card and fighting her but was easily overpowered due to her illness, causing the latter to defeat her.
- ↑ 1.0 1.1 You-Zitsu Light Novel and Anime — Volume 1, and Episode 3
- ↑ 2.0 2.1 2.2 2.3
- ↑ 3.0 3.1 3.2 You-Zitsu Light Novel and Anime — Volume 3, and Episode 8
- ↑ 5.0 5.1 You-Zitsu Light Novel and Anime — Volume 1, and Episode 2
- ↑ You-Zitsu Light Novel and Anime — Volume 2, and Episode 5
- ↑ You-Zitsu Light Novel and Anime — Volume 2, and Episode 6
- ↑ You-Zitsu Light Novel and Anime — Volume 4.5, and Episode 7
- ↑ You-Zitsu Light Novel and Anime — Volume 2, and Episode 4
- ↑ You-Zitsu Light Novel and Anime — Volume 3, and Episode 10
- ↑ You-Zitsu Light Novel and Anime — Volume 3, and Episode 12