- Shuuya Kano: Kano and Kido were put into the same orphanage and were eventually adopted together with Seto by the Tateyama family. Kano tends to tease Kido a lot, and gets hit or kicked by her as a result most of the time, since she doesn't show any tolerance for it. Even though he gets called an "idiot" by Kido a lot, they seem to be rather close friends. Kano describes Kido's past self as "cute," causing her to, often times, react violently towards him. When they were young, she gave him a scarf on their first meeting so that "there wouldn't be anyone dying in the cold".  They had both called each other by first name when they were young until Ayano's death. In the fifth novel sometime after Ayaka's death, Kido sees through Kano's fake smile and punches him, the pain reverting him to show his true expression. She then notes she will do that more often if she feels Kano isn't being honest. Of course, this isn't the only reason that she punches the boy. Most of the time, it's her reacting negatively and violently to his teasing and joking.
- Kousuke Seto: Seto and Kido were put into the same orphanage and were adopted together with Kano by the Tateyama family. In the fifth novel, Kido threatens to harm Seto at the orphange if he continued to address her with Keigo. There had always been a sense of conflict between the two of them, apparently. Sometime after Ayaka's death, Kido explains to Seto that she didn't like his polite speech was because her previous family made backhand comments using it, making her policy "Friends don't use Keigo". The two make amends and Seto adapts his speech pattern into a different variation. They get along quite nicely, and now live together in an apartment with their brother Kano, and the part-Meduse Marry. In the anime, Kido is shown to know Seto well, commenting that he is a worrywart despite not showing and excusing him to search for Kano.
- Marry Kozakura: Kido met Marry for the first time as Seto took her with him to her house. Marry became a member of the Mekakushi Dan not long after that.
- Momo Kisaragi: Kido met Momo when she walked across her crying in an alleyway by herself. Having been sent by Kano to search for her, due to her power, Kido then led her to the secret hideout and let Kano introduce Momo to the Mekakushi Dan. Momo became a member of the gang after that. On their first meeting, she made Momo faint when she tried to "make an impression" at Kano's suggestion. She is also seen taking care of Momo when she fainted in Otsukimi Recital.
- Takane Enomoto: Kido went with Kano, Shintaro and Ayano to Takane's culture festival. Both Kido and Kano decided to play in Takane's booth. Back then, Kido couldn't control her power yet, so Takane doesn't notice her until after introducing the game. Her power also activated while they were playing, causing Takane's cross-hair to disappear from the monitor.
- Ayano Tateyama: Ayano was told by her mother to be a "big sister" for Kido, Kano, and Seto. Ayano followed her mother's wish and started to become friends with the three of them, which turned out to be difficult, as they thought of themselves as "monsters" due to their eye abilities. Eventually, Ayano came up with the plan to create a secret club of heroes. Donning her red scarf, she announced the four of them as heroes- And members of a secret organization known as the Mekakushi Dan. 
- Kenjirou Tateyama: The adoptive father of Kido, Kano and Seto.
- Ayaka Tateyama: The adoptive mother of Kido, Kano and Seto. Gave the three of them their hoodies as a way to hide their eyes when their powers would activate.
- Konoha: In the manga, Kido tells Konoha about the Kagerou Daze and tells him to do what he thinks is best to help his friends. Before he leaves, she says that the group is there for him when he needs them.
- Rin Kido: The biological sister of Kido. She guided Kido to the exit of the Heat Haze and supported her when she was afraid.
- Hiyori: In the Manga, Hiyori and Kido meet for the first time in an alley, where 'Hiyori' proceeds to stab Kido, killing her.