Kazuki Uchida, son of Mr. Uchida, becomes Eriko Tamura's legal guardian after her father's death and her mother's coma. Childhood friends with a longstanding, familiar relationship, they share a close bond marked by Eriko's affectionate nickname for him, "Ka-chan," and her light teasing. Kazuki remains a consistent, supportive presence in Eriko's life as she transitions into the idol industry.

Over time, Kazuki develops romantic feelings for Eriko. He confesses these feelings, leading them to become an official couple. This romantic relationship is part of his character arc, positioning him as a supportive figure in Eriko's personal life alongside her professional challenges.

His primary role involves providing emotional support to Eriko, extending to her daily experiences and idol-related endeavors. His background as Mr. Uchida's son and his connection to Eriko's life both before and after the tragedy are consistent aspects of his character.