Karin Kaga is a fourteen-year-old female student who attends the same school as Lily Baker and her friends. Her birthday is on November 1st. Karin possesses an extraordinary talent for video games across various genres, particularly excelling in competitive titles where she often surprises even the most experienced opponents. Her ambition is to become a great professional gamer and participate in prestigious international tournaments. With the support of her older sister, she developed a unique avatar and started her own video game livestreams, becoming a popular VTuber without ever using the term herself, and as a middle schooler, she already receives collaboration offers from the gaming industry.

Karin considers herself an undefeated player in game centres, but her winning streak was abruptly stopped by a middle school student named Renji Kusakabe. She later discovered that Renji worked as a staff member at the same game centre where she had lost to him. Since that defeat, she has been resolutely determined to challenge and defeat him in future duels, though another match resulted in her losing once again. This drive to improve her skills and serve as Renji's rival defines a significant part of her character, with their relationship being marked by friendly competition. Her lively personality and passion for gaming are central to her interactions, and she often shares her victories and losses with her school friends, creating special bonds with them. Unlike her gaming prowess, Karin has some difficulties with studying and tends to tire easily during exam periods. Despite this, her commitment to gaming and her public streaming career showcase a dedicated and ambitious side, as she works to turn her passion into a pathway toward becoming a professional player.