|Drama CD||Ayana Taketatsu|
Mami Mizuno (水野マミ) used to be an antagonist but changed to a synagonist. She is also Shigure's and Hisame's childhood friend. She is young girl who becomes Yukina's rival for both Akira and Shigure, Mami suffers from a certain sickness since she was in such a young age, thus having Shigure care for her. She refers to herself as Mami instead of using "I."
Mami is a cute girl with medium length blonde hair with two slides on each of her bangs that reaches her shoulders and dark green eyes, sometimes colored blue. She always wears her 4 red hairclips. She is commonly seen wearing her school uniform.
Mami's personality when she first appears is that of a cute and well-mannered high school girl who's happy and innocent. However, Mami revealed that she can be sly, jealous, mean and possessive when it comes to Shigure which is seen when she has schemed multiple things in order to thrust him and Yukina apart e.g Telling Yukina if she ignored Shigure for a week she would tell her a secret about him. Mami in recent chapters though, has appeared to have realized her mistakes and has shown a more comical and friendly side to her personality instead of acting cute, she yells out her opinion of things. She even goes as far as to cheer for Akira and give him advice on dating as well as somehow ending up as Yukina's friend.
At first during the series, Mami had an intense dislike of Yukina due to the way Shigure would act around her and pretends to be really friendly towards her. When Shigure bit the nape of her neck for one of Yukina's missions. Mami states that "Naughty kids need to be punished" and informs Akira, Yukina's cousin and second love interest, about the mission involving the biting of Yukina's nape which leads to him wanting to do the same thing. Over the course of the series, Mami seems to have become more open with Yukina and she honestly becomes her love rival instead of scheming. She treats Yukina more as a friend and got angry at Hisame, her childhood friend, when he punched Yukina.
Shigure is Mami's childhood friend whom she developed feelings for. She appears to know about Shigure's secret of carrying a student notebook which includes names of the girls in his class and which he uses to keep track of how many girls have confessed to him and what methods have been used by them. She wasn't threatened by this as she knew that Shigure was never serious. She eventually confesses to Shigure, and though she is rejected, the two remain close friends. Mami is very close to Shigure and is very precious to him. He is also the only person aside from Akira who can comfort her.
Akira was the person who figured out about Mami's schemes against Yukina and Shigure and blackmailed her with the threat of telling Shigure about her schemes to do whatever he said. The two then are often seen together eating and talking and appear to be becoming quite good friends. Both have comforted each other on different occasions. Akira comforting Mami when she crashed into him in the corridor and when Shigure ditched her for Yukina and Mami has comforted Akira when he felt deflated about Yukina's involvement in Mami's confession with Shigure and also cheered him up when he felt bad about not walking to school with Yukina. In chapter 37 Akira tries to get her to tell him Shigure's weakness so he can win Yukina's heart but Mami stops him saying that if he used methods like she did he would end up rejected like her which leads to Akira acknowledging that she tried her best and smiling at her. Mami is shown helping Akira and even get's him to cut his hair in order to make him hot to help win Yukina's heart. In chapter 39, Mami is seen helping a Akira prepare for a date with Yukina and blushes when he smiles at her. It is heavily hinted that Mami may be falling in love with Akira. In chapter 40, it shows that Akira does not harbor any feelings for Mami. In chapter 47, Mami confesses to Akira that she wants to be his lover while Yukina sees, shocked. Recent chapters show that Akira is still wearing the hairpin that Mami gave to him in chapter 47 and as seeing that Yukina's feelings for Shigure is stronger then his own he seems to have started to focus on Mami. As of chapter 51, Akira asks Mami out and to be in a secret relationship with her. It was just an act, but in the end, Mami confessed that she actually loved him(chapter 58).
Hisame is Shigure's younger brother and he is one year younger than Mami. Mami calls him Hii-kun, and describes him as a mean guy who loves to bully her since they were children. She is very afraid of Hisame to the point of telling Akira to protect her from him in chapter 44, since Shigure won't be there for her because he went to his villa for the summer break.
Later, it is revealed that Hisame actually has feelings for Mami since they were kids. Proven when he gave the hair pins to her, but he lied and said that it was from her mother. The reason was because he doesn't want to see Mami cry. He was furious when he found out that Mami was giving some of the pins to Akira. He later confessed to Mami, it went kinda well at first but later Hisame said hurtful things about Mami's feelings so she rejected him and said that she won't love him the way he is now.
When Hisame was blackmailing Yukina, Mami and Akira set up a plan to stop Hisame and it worked. Hisame later says sorry to Mami and she accepted his apology happily, saying that Hisame becomes more mature somewhat. When Hisame learns that Akira rejected Mami, he hugs her and says, "I will become more mature and turn you around,".
Mami and Shigure met when Mami was admitted to one of Shigure's family's hospitals due to her illness. Mami's mother divorced her father and Mami felt that her mother hated her. She made a promise with Shigure that they would both avoid getting hurt by never falling in love. Though later both of them broke the promise since Mami was falling for Shigure and Shigure was falling for Yukina.
- Mami has a similar appearance to a vocaloid Rin Kagamine. Hair, eyes (they have either blue or green), and even hair clip.