| Relationships |
Saegusa Kasumi
She is incredibly close with her sister and calms her down when Kasumi loses her temper.
Saegusa Mayumi
Izumi looks up to her older sister Mayumi with respect and loves her very much. Izumi shows concern that Mayumi is wasting her youth because she doesn't have a boyfriend yet. However Izumi has shown that she is very protective of Mayumi, to the point she would know what boys are trying to get close to her and possibly scaring them away.
In Volume 17, Kasumi protests Kouichi's idea to have Mayumi pursue a romantic relationship with Tatsuya because it will ruin Mayumi's reputation and Mayumi would be view as seducer in other people's eyes.
Saegusa Kouichi
Izumi shares a good relationship with her father and is close with him.
Shiba Tatsuya
Izumi's first impression of Tatsuya was that he was someone to be cautious and wary around, and believes that her older sister (Mayumi) is in danger around Tatsuya because Mayumi is very casual and relaxed around him. However, Izumi begins to respect Tatsuya because she acknowledges his magical abilities and his consideration for other people like her twin sister (Kasumi). She considers him to be a bum because he leaves early from their work on student council. Katsuto once suggested to Tatsuya that he marry one of the Saegusa sisters to gain membership to the Ten Master Clans.
In Volume 17, Kouichi reveals to his daughters that Tatsuya and Miyuki are engaged and both of them belong to the Yotsuba clan, which causes Izumi to be shocked. Saegusa Kouichi asked her what she personally thought about Tatsuya. Izumi's reaction and choice of words were very interesting. When she talked about Tatsuya, she used very respectful words to describe him. It was similar to Hayama when he talked about Tatsuya to Mitsugu or Maya. Kasumi was shocked by her sister's reverence toward Tatsuya. Mayumi opened her eyes widely and turned to listen to Izumi's statement.
Izumi talked about Tatsuya's "stellar furnace", edited version of Phonon Maser and Invisible Bullet he created. She said Tatsuya was someone that she couldn't comprehend because she felt like he looked at matters differently from other people. She couldn't confirm if he had a unique eye similar to Mayumi's vision. Finally Izumi added that Tatsuya was not somebody that she could handle. She lost herself for a moment and added "If I had an ability to court / flirt with Tatsuya...... How can I let another man have Miyuki-senpai?" Even Kouichi grew concerned over Izumi's odd comment.
Hattori Gyoubushoujo Hanzou
It is revealed in the conversation of the Saegusa sisters in Volume 11 (Visitor III), Chapter The Ojou-sama's Magnificent Day off, that the twins either scared or threatened him, personally or more probably by an intermediary, for trying to approach or court Mayumi.
Shiba Miyuki
"Miyuki fit the imagined ideal of what Izumi ‘wanted to become.’
Izumi had fallen for Miyuki at first sight. She had gone so far as to ask Miyuki to be her "Onee-sama", and has once entertained the idea of having Miyuki as a sister in-law in the case that Tatsuya and Mayumi get married.
In Volume 17, Izumi is against Mayumi proposing to Tatsuya, because she assumes Miyuki may get mad. And also because the engagement was formally announced Mayumi's proposal to Tatsuya would make her sister be viewed as a shameless women and a seducer, but it's OK if Masaki proposed to Miyuki because Tatsuya will not get mad. She even thought it was a good thing that she can't be a match for Tatsuya, otherwise she'd have to marry Tatsuya and can't be with Miyuki. Izumi doesn't have that same reflexive 'cringe' of Miyuki being with a guy if it's with Tatsuya though.