Japanese Imperial Demon Army
Norito Goshi
As teenagers, the two butt heads, as he mocked her family for acting like they're all above every else, and said he'd "wipe the smirk off her face" once he became the head of his family in book 1 of the light novels. Mito would get annoyed by his teasing as well, shown when Goshi pokes at her when she scolds Guren for hiding his true strength. In book 4, Goshi shows care for Mito when saves and protects her from Guren once he witnessed him about to kill her, and they escaped the area together. Eight years later, they are on good terms, like she is with the rest of the team.
Sayuri Hanayori
Mito appears to have a very solid relationship with Sayuri, and in turn Sayuri shows great concern for her when wounded or hurt, as shown in the battle of Shinjuku where she came by her side and asked if she was okay. In the light novels, Mito has good admiration for her abilities as a bodyguard, and they soften up to one another after they all risk their lives for Guren.
Shinoa Hīragi
When her squad arrived late, Shinoa fought against her, Guren, and Shinya as punishment for their tardiness. She could easily fend off Shinoa's attacks and after winning the fight, Mito scolded Shinoa for her team's lack of teamwork, and called her an incompetent squad leader.
Shinya Hīragi
A friend from her high school days. Adopted into the prestigious Hīragi family. For this reason, Mito holds good respect to him as a Hīragi. She battles alongside him at Nagoya when Guren chooses herself and Shinya to battle against Shinoa and her squad. With Shinya they both later attempt to rescue Guren when he is captured.
Yūichirō Hyakuya
A 16-year-old soldier who gets special treatment from Guren. Mito is chosen alongside Shinya to battle against Yu and his squad as punishment for being late. She prevents his allies from backing him up by engaging them in combat and watches as Yu fights one on one against Guren.
Guren Ichinose
Like other people from prestigious clans, she initially looked down on Guren and participated in bullying him upon their first meeting. However, this changed after he saved her and Norito from Hyakuya Sect soldiers' attack on First Shibuya High School, to where she started to offer help in training him (believing that he was weak), and urged him to stand up for himself. After seeing his true strength, Mito was upset that he had hid it from her, and that he had simply taken the insults said by her and the other students on purpose. Despite Guren's answers that hiding his power was among his top priorities for the time being, she realized that if that were true, then he should have let Norito and herself die. The two later came to believe that Guren is a misunderstood and lonely person deep down. Mito eventually developed a crush on him, and in volume 6 of the light novels, she confessed her romantic feelings towards him. However, he maturely rejects her, but in a way so he would not hurt her feelings, and they both still considered each other as a very important companion to protect. Mito had always thought of Guren as someone, who she is deeply indebted to when believing that he has actually saved her multiple times.
When she is near the brink of being killed by the Hyakuya Sect, Guren rescued her, and Mito had compared him to that of prince charming in her mind. Even eight years later, she continues to have an infatuated, yet unrequited crush on him. Nevertheless, Mito tries to get involved with Guren whenever she possibly can if he is feeling depressed because he was the only one who treated her as a normal girl, unlike the strict policy within her family. Though their relationship still met with hostility every now and then, Mito began to show sympathy towards Guren and regrets the cold things she said to him in the past. This was shown when she grew worried about him and the things he is going through like his father's death. Another example was when she grew increasingly worried about the struggle Guren is going through, continuing to warm herself up to him. She is later shown to act against the will of her clan, such as when she and her squad go to Guren's home in Aichi Prefecture to comfort him after his father's death, and when she chooses to stay with Guren when he tells their squad that he intended to call Mahiru Hīragi for help, and those with him would probably be charged with treason, both of which would be subject to extreme punishment. In Vampire Reign, she acts like a classic tsundere to him, and interacts with him similar to their high school years, such as when she got riled up from Guren telling her to stop squeaking (which was one of the very first things he said to her). Like the rest of her squad, Mito is uncomfortable with Guren refusing to answer what burden he is carrying that lead him to slaughter their own soldiers, saying their squad was all family and believed they should share it.
Shigure Yukimi
When sixteen, Mito initially poked and made fun of her for serving under the Ichinose clan, deeming them weak. Shigure also showed disdain to her for insulting Guren. It wasn't until their first duel Mito began to show respect to her, and complemented her fighting abilities. She even recommended Shigure to leave the Ichinose clan and serve under the Jujo clan instead, although Shigure declined without a second thought. Though they don't interact much, she gets along with her well.
Vampires
Mel Stefano
Guren's squad kills him in Nagoya.
Other
Mahiru Hīragi
In high school, Mito completely adored Mahiru and was very proud to be working under her. Mito went as far to refer to her as a "goddess" for her beauty and kindness towards others, and strongly admired her strength. Now, as Guren's weapon. She was killed by Mahiru and the rest of Guren squad (except Guren) prior to the apocalypse. It's unknown how she feels about her eight years later.