May calendar.

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Mark Anatolyevich (a teacher from the past): An important character the kids meet when time "rolls back" far into the past. He's the only adult who trusts the kids and helps them understand the laws of time.

The class teacher, Svetlana Alexandrovna, is a typical teacher who only sees the superficial side of children's behavior. She considers Gleb a troublemaker, Yura a diligent student, and Lena a withdrawn girl with poor academic performance. At the beginning of the book, she doesn't realize that their behavior is rooted in deep personal dramas.

Lena Zyuzina's mother: A woman exhausted by daily life and poverty. While Lena's father is in prison, her mother works several jobs to support her large family. She loves Lena, but lacks the energy for emotional intimacy, so she views her daughter primarily as an adult helpmate, not as a child.

Yura Karasev's mother and grandmother: An example of overprotectiveness. His grandmother constantly bakes pies, which Yura uses to "eat away" stress, and his mother controls his every move. They prevent Yura from growing up, causing him to grow up dependent. The death of his grandfather, which Yura tries to prevent by going back in time, becomes his most difficult ordeal.

Gleb Elizarov's father: A lieutenant colonel, a strict and disciplined man. After the death of Gleb's mother, he remarried to Vera, a doctor, giving Gleb a stepmother and a little sister. His father ignores his son's loneliness, believing he provides for him. Gleb, for his part, views his father's new family as a betrayal of his mother's memory.

Stas Mokhov
Role and personality: An athletic, popular guy who often partners with Vera. He's the leader of the "successful" part of the class. He has black hair, blue eyes, and a prominent, humped nose.
Attitude toward the characters: For him, Gleb, Yura, and Lena are "losers." He doesn't display overt cruelty, but maintains a general atmosphere of irony and ridicule toward them (especially regarding Yurasik's appearance).

Vera Nesterova
Role and character: The class's beauty and star. She's confident, a little arrogant, and used to being the center of attention. Vera is Lena Zyuzina's antithesis. She's blonde, has blue-gray eyes, and fair skin.
Relationship to the characters: He treats the trio with condescension. At the beginning of the book, Gleb tries to attract her attention and even has a slight crush on her, but during the "reverse days" he realizes that Vera is shallow and self-absorbed, while Lena is a genuine and profound person.

Lena Zyuzina
Appearance: A tall, thin, awkward girl with sad eyes. Usually dressed simply and poorly, she has waist-length red hair, blue eyes, and freckles on her nose.
Personality: Responsible and prematurely mature. Lena comes from a large family, where her father is in prison and her mother works several jobs. Lena is the one running the household and caring for her younger siblings, so she has "no time for friendship." She's withdrawn and used to relying only on herself.
Relationships: Lena brings practicality and caring to the team. At first, she avoids the boys, believing them to be the cause of her problems, but later realizes that they are the only people who truly need her. She learns to allow herself to be just a child, not just a "nanny."

Yura Karasev (Yurasik)
Appearance: A plump boy with glasses, which often makes him the object of ridicule among his classmates, he is plump, has brown eyes and dark hair with curly hair.
Personality: A typical "nerd," highly intelligent, erudite, and sensible. Yura lives in an overprotective environment from his mother and grandmother, which makes him dependent and cowardly. His main pain in the book is trying to save his grandfather, whose death inexorably approaches as time ticks backward.
Relationships: Yura is the "brain" of the trio. He analyzes the situation, searches for information about the Mayan calendar and ways to stop the loop. Over the course of his adventures, he becomes much bolder and learns to make independent decisions, no longer being a "mama's boy."

Gleb Elizarov
Appearance: A typical sixth-grader, often looks cocky or dissatisfied, blue-gray eyes, short brunette hair, thin but strong, loves football, pale skin.
Personality: The son of a military man, accustomed to moving around. At the beginning of the book, he appears to be a conflicted, quarrelsome, and lonely teenager. Gleb often bristles to hide his resentment toward his father (who started a new family after the death of Gleb's mother; his father found a new girlfriend, Vera, who works as a doctor). He is decisive, prone to risk, and possesses leadership qualities.
Relationships: He is the one who initiates the "crime" (the inscription on the stone) that triggers the countdown. At first, he treats Yura and Lena with disdain, calling them "defective," but gradually learns to trust them, protect them, and value their friendship.