Hikari is the protagonist of the story. She holds the 2nd position in school for having the best grades. Self-proclaimed as Kei Takishima's greatest competitor, she is determined to beat him in any kind of competition. Stubborn, proud and hot-headed, Hikari never backs down from a challenge, especially one from Kei, because she is constantly looking for an opportunity to surpass him, though has never done so. A kind girl who always worries about others, Hikari sometimes lacks common sense. She is good at sports and academics, but she is very bad at teaching,cooking, and sewing. Although she can handle her own in a fight (often against boys), Kei, nonetheless, gets irritated whenever she puts herself in danger. Although Hikari is rather sensitive to others, she is quite dense when it comes to love. She is oblivious to the romantic feelings Kei has for her, though everyone else knows that Kei is in love with her. In volume four Hikari begins to fall in love with Kei, though she does not realize it until volume six. Along with Ryuu, Hikari also knows Finn's real gender.

Ranked first in school for having the best grades, Kei is the son of the CEO of Takishima Corporation. As Hikari's undefeated rival, he likes to refer her as "Number Two", which never fails to provoke her. He has a photographic memory and the ability to do anything right on his first try. He usually prefers to do things on his own until Hikari shows him how much fun it can be to work together with others. Kei is in love with Hikari, a fact that he does not deny, and has loved her since they were children. However, he has not confessed his love to her because he knows that Hikari does not understand those feelings and would think that he is referring a love between friends. Although he is stoic most of the time and always maintains a calm facade, things involving Hikari can bring intense anxiety out of him. It always bothers him whenever Hikari pushes herself too hard or causes trouble, but her strong will and determination are the reasons why he admires and respects her.

Jun is ranked 3rd in school and is Megumi's younger twin brother. The son of a music producer and a talented singer, Jun loves music more than anything else, but ironically has little talent for music. He is usually nice, but he has a split personality which he has concealed from everyone except Megumi and Ryuu. Triggered whenever he is kissed by a girl or receives a lot of affection, he becomes a bad boy, which is the complete opposite of his true self, and becomes irresistible to nearly all women. His split personality resulted from an hypnotism program that Jun watched as a child and first emerged when he was still in grade six. During a date with a girl, he changed and all the other girls around him became mesmerized by him; this led the girl Jun was dating to hate him and call him disgusting. The only thing that can bring him back to his original self is Megumi's horrible singing voice.

Megumi is ranked 4th in school and is Jun's older twin sister. She is the daughter of a famous vocalist and music producer and shares her brother's love of music, but, like Jun, she does not possess any musical talent at all. A cute and nice girl who rarely joins in disputes, Megumi is always quiet and refuses to speak because of her bad singing voice. She usually writes on a sketchpad to communicate with others, but will speak when deeply upset, which can have devastating after-effects. The only person she is seen speaking normally to is Yahiro, because she harbors feelings for him. Like Jun, she is very close to Ryuu; she can be fiercely protective of her brother and Ryuu. Megumi also happens to be bad at sports and dislikes them.

Innocent and carefree, Tadashi is ranked 5th in school. His mother, a fierce and intimidating woman, is the director of the school and the primary reason why he is in the SA; she told him he would be allowed to do whatever he wanted if he became a member of the SA. He suffers from wanderlust and frequently likes to vanish on some journey and return later for special school events. Tadashi is smarter than he looks and acts, though is usually the character who is most often comically attacked (frequently by Akira and Kei) because of his careless comments or reckless behavior. He likes Akira, but often makes rude, weird, stupid or inappropriate comments that provoke her to beat him up. Tadashi also seems to enjoy playing with puppets, is fond of Akira's cooking, and appears to like being beaten up by her.

Akira holds the 6th position in school and is the daughter of the owner of an airline company. She is very fond of Hikari and cute girls, but apparently dislikes Kei, even though they are childhood friends. Akira is very enthusiastic about her afternoon tea, and has even constructed her own kitchen on campus. Akira apparently loves Tadashi, but never seems to hold back when hitting him for teasing her. In chapter 37, she finally confesses to him, and he tells her he returns her feelings.

Because of Akira's parents, she often played with Kei and Yahiro during her childhood days. She was surrounded by the most powerful people in kindergarten, so nobody dared to approach her, since the two are very protective. She used to envy all the other girls who were able to play freely. She was good friends with Yahiro as a child, but due to a misunderstanding resulting from Yahiro's protective and somewhat selfish behavior, she avoids him whenever possible. Her dislike of him stems from Yahiro causing her childhood friend Sayo to despise her when her family had to move away; since Yahiro never told her that he had discovered Sayo had only befriended Akira because she was rich in order to protect her, Akira continues to blame Yahiro for the loss of Sayo.

Ryuu holds the 7th position in school, although his test scores are a poor reflection of his intellectual prowess. He is in 7th place mainly because of the twins - Megumi tends to fall asleep and Jun becomes bored during the test, which results in Ryuu focusing the part of his attention on them instead of his own exam. He has been close to Megumi and Jun since they were very young; it is evident that he cares for the twins very much and it is stated that Jun is his favorite among the twins. He loves animals and is good with children. Along with Hikari, Ryuu is one of the few people in the world who knows Finn's real gender. He is the son of the CEO of a sports company and one of his family's clients is Yahiro's family.