If you watch the drama after looking at the character relationship chart for Manager Kim,

According to the released character relationship chart, various characters appear in addition to Department Head Kim, Park Jin-cheol, Seong Han-soo, Kang Kuk-cheol, Jeong Sang-ah, Kim Min-ji, and Ju Kang-chan. So Ji-sub plays Department Head Kim of the Accounting Team at Sangsaeng Savings Bank. Having lost his wife, he is raising his daughter alone and constantly feels sorry for her for growing up without a mother. One day, while his ordinary life continued, his daughter Min-ji disappears, and to save her from danger, he reveals his identity, which he must absolutely keep hidden.