When Hee-Do and her online friend (who is Yu-Rim, unbeknownst to her) agree to meet in person for the first time, they agree to meet at the park with a yellow rose in hand. Worried that whoever Yu-Rim is about to meet is a predator, Yi-Jin accompanies her to go meet Hee-Do. But when Yu-Rim realises her online friend is Hee-Do, afraid to reveal her identity, she panics and gives the yellow rose to Yi-Jin.
When Hee-Do sees Yi-Jin with the rose, Hee-Do tells him, "I have to have you." Yi-Jin says he's not the person Hee-Do was looking for, which causes her to become flustered and run away embarrassed. Hee-Do ignores Yi-Jin for the next few days and eventually confesses she doesn't know exactly how to feel about him. Later, she compares her relationship with Yi-Jin to a rainbow.
Image Source: YouTube user TvN Drama