Based on a popular 2017 Web Novel of the same name, it tells the love story between a lovely "sunbae" and a bold "hoobae".

An AI programmer accidentally develops an AI program called Cho Sang Shin, which will identify trashy humans, and she uses it to save people who are in difficult relationships.

A man and woman who were in love in their 20s meet again in their 40s, and find that they've both become different people during their years apart.