Haruhi Suzumiya First person: I (energetic, casual) Class 2-5 Height: 158cm A beautiful girl with short black hair. She is an all-rounder in sports and excels academically. Although Haruhi herself is unaware of it, she possesses the ability to change the world according to her own will, and the members of the SOS Brigade work day and night to prevent her powers from awakening. While she is a beauty when silent, her personality is self-centered, arrogant, reckless, and extremely competitive. To put it bluntly, she is haughty and egoistic. She also possesses diverse talents in cooking, playing instruments, and singing. Even Kyon admits she is a woman of great beauty and talent, saying "she has no flaws except for her personality."

Kyon First person: I (casual, blunt) Class 2-5 Height: 170cm The reason he is called Kyon is that his younger sister started calling him "Kyon-kun" for fun, and an acquaintance heard it and spread it. His personality is characterized by a desire for peace and quiet, and his catchphrase is "Good grief." He is the only person who can properly argue with Haruhi. Although he is calm and his emotional fluctuations are not very intense, he is a good-natured man of common sense (the straight man role) who will give a serious lecture or run around to help his friends. Unlike the other SOS Brigade members, he has no special abilities. He is always on the verge of failing his periodic exams and has the worst academic performance in the SOS Brigade.

Yuki Nagato First person: I (flat, polite) 2nd Year The only member of the Literature Club at North High, who was forced into the brigade when Haruhi took over the club room. She has short gray hair and wears a gray cardigan. According to Haruhi, she is the "essential silent character for the SOS Brigade." Her true identity is an alien. She possesses information manipulation abilities. Even when she speaks, she only talks in short, detached words. She has a strong appetite for knowledge and food. She is always reading a book of some kind. She is flat-chested.

Mikuru Asahina First person: I (soft, polite) 3rd Year The Associate Associate Brigade Chief of the SOS Brigade. She is the only upperclassman, kidnapped by Haruhi to serve as a "loli, large-breasted mascot character." She is beautiful with long brown hair. She is shorter than Haruhi and Yuki Nagato but has large breasts. While her personality is serious and kind, she is also introverted, a crybaby, and a klutz. She is a time traveler from the future and also serves as an observer for Haruhi. Since she is a low-ranking member below a trainee and has no authority, she only responds with "That is classified information" when asked about information from the future. She is treated as a toy by Haruhi and is made to do various cosplays every time. Since Haruhi forces her to wear a maid outfit in the club room, she is often seen wearing one while serving tea to Kyon and the others.

Itsuki Koizumi First person: I (polite) Second person: You / [Surname]-san Class 2-9 Height: 179cm A male student and the Deputy Brigade Chief of the SOS Brigade. Because he transferred in at the odd time of May during his first year of high school, he was recruited into the SOS Brigade by Haruhi as the "mysterious transfer student." He always has a smile on his face, is mild-mannered and refreshing, and always uses polite language with everyone. He is in the specialized science and math track class. He is smart and has good athletic reflexes. He belongs to the "Agency," an organization of espers. He has the ability to enter "Closed Spaces" generated by Haruhi's unstable mental state and attack the "Celestials" that cause destruction within them by manifesting as a red orb of light. Due to his duties, he pays close attention to Haruhi's mental state and is basically a yes-man to avoid provoking her. According to himself, his current personality and expressions are an act tailored to "Haruhi's desires."