Mikado is introduced as the Septimal Moon member that was closest to Seimei Aoyagi. Having said that, she emphatically states that their alliance is in the past tense. She mentions that Ritsuka looks like Seimei from when Seimei was 12, implying that she knew Seimei during their childhood.
When Loveless and Moonless return to Soubi’s apartment, Mikado asks Ritsuka if he is interested in creating an alliance with Moonless to bring down Seimei. Ritsuka refuses, insisting that he was searching for someone who understood Seimei. Mikado, a little surprised and more than just a bit displeased, is forced to explain one of the reasons why she wants to bring down Seimei.
In volume 11, Mikado states that she and Seimei both cannot control their emotions— or rather, they lack emotions. Their mutual apathy towards others was the main reason why they initially got along so well. She removes her cap at this point, and reveals that the pigtails are actually a wig. Her hair is cropped short, giving her a mature appearance.
Tokino interjects here, and explains that Mikado is convinced that she has no emotions due to her home life. Mikado insists that it isn’t the main problem.
Mikado then moves on to explain that Seimei ordered Nisei Akame to cut her hair off and rape her. Mikado, however, denies that she is angry about how she was abused. Rather, she states that she wants revenge for not receiving a reason. “For me,” she says, “For me and Seimei-san, there is nothing. We can’t quite figure out our own feelings, or other people’s. It’s also true for pain. But with a reason, we can understand. To be connected with other people and the world, we have only that. A reason is such an important thing. Everything can be summed up in a reason. But despite understanding how important a reason is for both of us, he didn’t give me a reason. I have a grudge against him for that. It’s treason against a kindred soul.”
Since this incident, Mikado always wears a wig and a cap to cover up the loss of her hair and ears.
Mikado once again offers an alliance, but Soubi stops her, shouting that Ritsuka didn’t need to hear such things. Tokino flies into a rage at how Soubi refers to Seimei's betrayal to Mikado as "such things", but Mikado stops him by calling him an idiot. After another argument with the Zeroes, and an reaffirmation of what a “reason” means to her, Moonless departs without having made a suitable conclusion to their alliance offer.
The next scene has Mikado standing in front of a window, surveying the city from a high apartment room. Tokino offers her a parfait for breakfast, joking that she’ll gain weight quickly if she continues to do so. Mikado smiles it off, and states that she only eats sweets in the morning, as so not to grow plump. She then requests iced coffee, which Tokino supplies before informing Mikado that he had contacted Faceless for information on Beloved. She is slightly concerned with their mercenary motives, but accepts the information Tokino received.
During the events in which Soubi is lead away by Seimei, Mikado is seen making a comment to herself about how she loathes rats. It is implied she is aware of Nisei's wiretapping, which is how she knew where to find Nisei.
A few days after Soubi was reclaimed by Seimei, Moonless traps Nisei within their battle area, which takes the form of an illusionary room with luxurious curtains and a throne for Mikado. Mikado orders Nisei to call Seimei, despite Nisei saying that Seimei will not come. Surprisingly, Seimei does appear. He offers Mikado a choice of battling either Nisei or Soubi—she replies that it makes no difference, seeing how Tokino is her “undefeatable knight” and that Moonless cannot be defeated by Beloved because they have a bond of trust Seimei couldn’t understand. Moonless then unanimously chooses Nisei for the first round of the battle, and subsequently defeat him within minutes.
Mikado seems to be taken back by Seimei's treatment of Nisei, questioning Seimei why he sent Nisei to fight alone. Although Mikado does not care about Nisei's personal health, she seems to be disgruntled by the way Seimei treats his supposed other half. She puts heavy emphasis on the importance the Fighter/Sacrifice bond and flaunts her victory by kissing Tokino's hand.
After Nisei's defeat, Seimei orders Soubi to fight against Moonless. Mikado agrees to the challenge, apparently indifferent to Nisei's humiliation.
In the special booklet from Volume 11, Perfect Days, it is revealed that Mikado and Seimei were in "perfect harmony," needing no words to understand each other. A notable memory of the two sitting back to back and eating together is shown while Tokino tries to find shoes that suits Mikado best. Constantly throughout the shopping trip, Mikado disparages Tokino for his inability to understand her feelings, making fun of his overprotectiveness. Even so, she confesses that she thinks it's fine for him to be "stupid" as long as they are together.
- Her first name and her last name share the same kanji.
- Mikado signs her name at the end of her text messages.
- Ritsuka initially believes that Mikado is younger in age than he.
- Mikado's feet size are 22.5 cm.
- Mikado mentions that Ritsuka looks exactly the same as Seimei did when Seimei was in sixth grade, implying that she knew Seimei for a rather long time.
- Mikado may be the "4" Nana mentioned to Ritsuka in one of the Wisdom Resurrection sessions, seeing how she was both Seimei's closest "friend" and the one in charge of executing him. Furthermore, the number "4" in Japanese can also be pronounced as "shi," which is homophonic with the Japanese word for "death". This is linked to the idea of Mikado being the one with the duty of murdering Seimei.
- Mikado is described as "the rain girl," because rain seems to follow her wherever she goes. This is also said to be extremely helpful during nights, since the moon is hidden by the rain clouds. However, Mikado herself finds constant rain "tiring."
- She states that she doesn't hate Seimei, and doesn't care what Tokino does to him.
- Mikado also states that the only way to be connected to the world is a "reason," which is why she is so intent on capturing Seimei—he had not given her a reason, although he, out of all people, understood perfectly how important a reason is to the two of them, thus betraying her.
- Mikado explains that Moonless estimates their attacking power at "10," leaving their defense at "0." If there is a counterattack, then they are wiped out.
- In Tokino's battle area, Mikado is seated on a throne.
- Mikado calls Seimei a "fucking piece of shit."
- In the same chapter, Mikado calls Tokino her "undefeatable knight," when given a choice of battling with Nisei or Soubi.
- Soubi notes that Moonless's bond is based on trust.
- In Perfect Days, Mikado is seen without a cap.
- The story that Seimei Aoyagi tells in the Septimal Moon's library may be referencing Mikado's rape and consequent betrayal.