Contains spoilers for this episode and earlier episodes.
Dal-mi develops business ideas while Won-deok worries that she will suffer the disappointments her father faced. In-jae gathers employees willing to leave her former company and tries to build without her stepfather's support. At a bookstore, Dal-mi bargains with lawyer and designer Jung Sa-ha over a guide to Sandbox. Do-san's company attracts visitors after its competition success, but Ji-pyeong intervenes when supposed investors try to obtain the programmers' technical secrets.
The invented birthday in Dal-mi's letters creates another problem for Do-san. Ji-pyeong coaches him for a formal date, only for Dal-mi to reveal that her imagined childhood friend wanted to play Go-Stop. They improvise a gathering in Ji-pyeong's apartment, dressed as Samsan Tech's office. Afterward, Do-san asks why she likes him. Her childhood memories and the letters belong to Ji-pyeong; her affection for his large hands is something Do-san can claim for himself.
At Sandbox, the applicants compete for the chance to lead teams in a hackathon. Dal-mi and In-jae qualify as prospective chief executives, while Do-san fails to secure that role. Both sisters approach Samsan Tech, forcing the programmers to choose between In-jae's experience and Dal-mi's offer to join their existing company. Do-san points out that Dal-mi wants to work with them rather than absorb them into her team. The founders choose her, and she accepts their invitation to become chief executive.