From the letters she wrote and how she acts at home, Tomoe is bit hasty and pushy with others, especially her little brother Hōtarō. It is unknown if she acts like this to all people, but it is displayed when she gives a broken fountain pen to Hōtarō when he desired some kind of good luck charm.
Tomoe has long brown hair and seems to be a bit shorter than her brother Hōtarō. Her eye color is somewhat greenish or could be the same color as Hōtarō. Her face is almost fully revealed and it was shown during the Kanya Festival when she's about to check how Houtarou's doing. She wears a variety of styles for casual clothes from simple tops and short pants at home to colorful attire when going out.
While much is not known about Tomoe yet, she plays an important role in the series, often contributing to the circumstances her brother Houtarou would face at school. By the start of Houtarou's second year in high school, Tomoe is in Banaras in India, en route to Sarajevo in Bosnia and Herzegovina. In one of the letters she habitually sends to Hōtarō, she told him to join the Classics Club. Although Houtarou is quite lazy and refuses to join, he eventually reconsiders because he knows that his sister "would make it very painful to refuse". Eventually, her letter would allow the Classics Club to form once more, and she intervenes once again, this time in a case involving the issue of the Hyouka anthologies of 45 years ago, when she mentions the location of old anthologies from the Classics Club.
Tomoe maintains contact with Houtarou by mail or by phone and later pushes Houtarou in a case involving the amateur film of Class 2-F for the Kamiyama High School Festival by referring him to the third year Fuyumi Irisu. She later warns Irisu about messing with Houtarou following the developments of the case.
Soon enough, she comes home, just in time for the day of the school festival. Tomoe even participates in the "Straw Millionaire" situation Houtarou found himself in, by giving Houtarou a fountain pen, and later trading Houtarou's hand mirror for a copy of "A Corpse at Night", which Houtarou later required to solve the Juumonji Incident.
Tomoe's personality seems wild, active and ambitious. She enjoys traveling and has traveled alone across the continent of Eurasia at the time of her college enrollment, and even had the experience of climbing a 2000m mountain. As a martial arts expert in Aikido and Taiho-jutsu and a proficient university student, she "was not content with conquering Japan alone, and had decided to go out and challenge the world." Throughout the novel, she travels around the world, from New Delhi to Beirut and so on. Readers also learn that Tomoe asked her little brother to join the Classics Club because she was a member in the past. It seems that she has a connection with Jun Sekitani because, in a brief phone conversation, she is able to give Hōtarō a clue about the uprising Jun Sekitani was connected to 45 years ago.
As his old sister, Tomoe has a warm family love for him, even though Hōtarō himself is not fond of it and normally acts more bored than usual like if he was trying to ignore her. Although he seems to fear her in other ways, knowing that if he had attempted to reject Tomoe's request join the Classics club, he would face something painful.
Due to being able to give some hints to Jun Sekitani's connection to the events of 45 years ago, Tomoe may have possibly been an aquaintance.
- In the Kanya Festival, Chitanda and Tomoe share eye contact in a hallway and Chitanda said: "I feel like if I've seen that look before." Hinting that Tomoe's eyes resemble Hōtarō's.
- In End Credits of The Fool, Hōtarō mentioned that the book about Tarot Cards from his bookcase belongs to his sister. Since Tomoe was part of the Classics Club, most of the books probably belongs to her but she left her bookcase to her brother.
- It is also hinted that she may have connections with the other characters in the anime, unknown to Hōtarō. Like Fuyumi Irisu, based on their chat as she called Hōtarō as "the idiot".
- It's worth noting that she and Hōtarō are based on Sherlock and Mycroft Holmes with interchanged traits. Hōtarō almost never does any mystery solving despite having the gift to, until he met Chitanda, Eru; A trait akin to Mycroft. Meanwhile, Tomoe is implied to have the same gift but is more adventurous than lazy, similar to Sherlock. The two traits aside, Sherlock was also not without any knowledge of martial arts or self-defense like Tomoe. Oddly though, Hōtarō is the one who has a sidekick and the level of deductive reasoning is flipped between the siblings, with Tomoe having Mycroft's level of intellect and Hōtarō of Sherlock's. Possibly a play in references as Sherlock Holmes is also referenced a number of times within the whole series.
|Koten-bu series and Hyouka Featured Characters|
|Main characters||Eru Chitanda • Houtarou Oreki • Satoshi Fukube • Mayaka Ibara|
|Students||Ayako Kouchi • Fuyumi Irisu • Jirou Tanabe • Junya Nakajou • Kaho Juumonji • Koreyuki Tani • Kurako Eba • Masashi Toogaito • Mayu Hongou • Misaki Sawakiguchi • Muneyoshi Kugayama • Shouko Yuasa • Tomohiro Haba • Yasukuni Yoshino|
|Other||Jun Sekitani • Haruna Anjou • Kayo Zenna • Masakiyo Ogi • Omichi • Rie Zenna • Tomoe Oreki • Youko Itoigawa|