Kinko Echigoya is one of the Echigoya sisters, alongside her younger sister Ginko. Both bear names reflecting immense wealth: Kinko meaning "gold child" and Ginko "silver child." Fifteen years old and a third-year junior high student, Kinko attends the same school as Ginko and serves on the student council, potentially destined to inherit her father's corporate empire.

She presents polished manners and a friendly face, yet possesses a strict, difficult-to-approach personality. Despite her family's fortune, Kinko obsesses over bargains and discounts, delegating the daily hunt for supermarket deals to Ginko regardless of effort. This baffles observers like the financially struggling Yamada sisters.

Her relationship with Ginko begins strained by mutual misunderstanding. Kinko believes Ginko dislikes her, while Ginko feels she constantly disappoints her sister and struggles to measure up, creating tension contrasting the Yamada sisters' closeness. Kinko's approach includes missteps like preparing an inedible lunchbox filled with random, poorly combined ingredients for Ginko.

Over time, Kinko's interactions and Ginko's covert observations of the supportive Yamada sisters foster gradual improvement. Ginko seeks Asu Yamada's advice, leading to better understanding. While complex, their relationship becomes somewhat more reconciled as they navigate differences.

The sisters keep a pet alligator named John, adorned with a bow ribbon, in their garden. They serve as narrative foils to the Yamada sisters, highlighting differing socioeconomic statuses and family dynamics while exploring sisterhood and communication.