Sanjo Yukari is a former employee of of Easter Company, the older sister of Sanjo Kairi, and Utau's manager. She came up with a new project, Black Diamond, to find the Embryo and mass-produce X Eggs. The CDs of the band were freely distributed and the people listening to it had their Eggs removed by force. As the band became more famous, their song is slated to be released to the Internet together with the unveiling of the band.

She and Utau resigned from Easter after Amu got Diamond back, and started their own music industry called Sanjo Productions. Yukari once dated Nikaidou Yuu, but the two have since broken up. She gets annoyed whenever their relation is mentioned.

Nikadou Yuu

Nikaidou Yuu is a former employee member of Easter. In order to find the Embryo, he joined Seiyo Elementary and became in charge of Amu's class in the disguise of a ditzy but kind-hearted teacher. His childhood dream was to become a robot engineer, but when his mentor quit, due to his ailing wife, and his parents opposed the idea, he lost sight of his dream and became a twisted person. He recovered with help from Amu and Su. He resigned from Easter Company and officially become the teacher in charge of Amu's class. A running joke is that he calls Amu Himamori, meaning "leisure time". He dated Sanjo Yukari before the series began, and they broke up.

Sanjo Kairi

Sanjo Kairi replaces Kukai as the new Jack's Chair when Kukai leaves for middle school. Kairi is tall, despite being two years junior to Amu. Unlike the spontaneous Kukai, Kairi is uptight, very organized, and blunt about faults. Even with these traits, he is so capable that Amu and Yaya call him "class president".

Kairi is the younger brother of Sanjo Yukari and was sent to spy on the Guardians. This wasn't his choice though, Yukari immediately begged him to transfer to Seiyo upon discovering that he had a Guardian Character. Since his sister is busy at work, Kairi takes care of the household work (and his sister) in her apartment. However, when he saw the true meaning of his "missions," he tries to rebel against Yukari, but not before he reveals his secret to the guardians when they accidentally discover him with Pestering CDs. He switches sides, after Amu convinces him he is a good person. Afterward, he leaves saying that he promised his parents and local classmates that he would return, but not before declaring his love for Amu saying that he shall return for her when he has become a man. He also declared a rivalry toward Tadase.

Mashiro Rima

Mashiro Rima replaces Nadeshiko as the new Queen's Chair. Although Rima is the same age as Amu, she is extremely petite and has relatively poor athletic ability. Most of the boys in her class admire her because of her beauty and passive personality, while the girls are annoyed by her because of her selfishness.

Because of a kidnapping incident that happened before she transferred to Seiyo Elementary, her parents pick her up after school, but since it interferes with their work schedules, they often argue about who cares more for Rima over work, resulting in Rima often having no one but Kusukusu as company for her secret interest in gag comedy. Later, she opens up to Amu and becomes friends with her.

When Yaya explains to Rima about Amu and Nadeshiko's friendship, she is shown to be jealous. At first, she is shown to have great dislike for Nagihiko because Amu told Rima and Yaya that he is Nadeshiko's twin brother due to a confusion between the two. That leads Rima to be protective over Amu. She tells Nagihiko that he is useless because his Guardian Character is still inside an egg, but gains respect for him later on.

Yuiki Yaya

Yuiki Yaya is the childish girl serving as the Ace Chair and is one year junior to Amu. Yaya often acts immature for her age, such as having an enormous sweet tooth, a great soft spot for items like ribbons as well as tending to be hyperactive. She is also a ballerina, though a rather clumsy one. She has a newborn baby brother named Tsubasa, who, she claims, gets all her parents' attention. It is because of this that her baby-like Guardian Character, Pepe, was born. Though she acts jealous around Tsubasa, Yaya does have a responsible side, once personally taking him to the doctor when he had a fever, as no other option was possible.

Souma Kukai

Soma Kukai is the upbeat, energetic, and friendly Jack's Chair of the Guardians. One year senior to Amu, Kukai helps Amu with her training as the Joker. Although he was the captain of the soccer club, Kukai loves and excels at all sports. At the end of the school year, Kukai graduates and goes on to middle school. However, Kukai returns to visit the Guardians from time to time.

Fujisaki Nadeshiko

Fujisaki Nadeshiko is a student in the same year as Amu and serves as Queen's Chair of the Guardians. When Amu rejected the offer to join the Guardians, Nadeshiko tries several tactics to convince Amu to join. The two become best friends and Nadeshiko looks over and supports Amu in her love life. However, before Amu and Nadeshiko enter the sixth grade, Nadeshiko leaves Seiyo Elementary for Europe to study dancing.

Nadeshiko is actually a boy named Fujisaki Nagihiko, called "Nagi" as a nickname by Amu and the girls. It is tradition in the Fujisaki family for males to be raised as females as part of their training so that they may play female roles in Japanese dance. Nagihiko's secret is known by his family, Kukai, Tadase, the school's principal Tsukasa Amakawa, and as of chapter 34, Rima. After Kairi leaves the Guardians, Nagihiko returns and is appointed as the interim Jack's Chair.