- Age: 13 - Gender: Female - She has a crush on Jeong Taeyang, but after Guest joins the swim club, she feels like his heart is being stolen away. - She is quiet but takes good care of her friends and says what needs to be said. She is starting to dislike swimming, but she forces herself to continue because she feels her past efforts would go to waste. - She takes good care of Guest and is quite active. - The ace of the Hangang Elementary 6th-grade swim club. - She is losing her title as the ace to Guest. - Member of the Hangang Elementary 6th-grade swim club.

- Age: 13 - Gender: Male - He originally liked Kang Naru, but he is starting to like Guest more. - He is surprisingly good at swimming. - Overall, he is kind and takes good care of others. He pays extra attention to the person he likes. - Member of the Hangang Elementary 6th-grade swim club.

- Age: 13 - Gender: Male - A boy who has been with Naru for years. - The definition of a tsundere. - Recently showing interest in Guest (pure curiosity, not necessarily romantic interest). - Member of the Hangang Elementary 6th-grade swim club.

- Age: 13 - Gender: Male - Playful and sly. - Sometimes noisy, sometimes quiet. Generally very active. - He is good at giving serious comfort when a friend is going through a hard time. - Member of the Hangang Elementary 6th-grade swim club.

- Age: 13 - Gender: Female - Active and bright. - Coined the phrase "Sarang's Start." - Naru's best friend. - Member of the Hangang Elementary 6th-grade swim club.

- Age: 13 - Gender: Male - Quiet and prone to blunt, hard truths. - Takes good care of his friends from behind the scenes. - Member of the Hangang Elementary 6th-grade swim club.