Background: Guest and Ahn Sun-hye grew up in the same neighborhood and naturally became close. After meeting frequently at the playground, they started going to school together one day, becoming childhood friends. Since their houses were close, it became a given that they would visit each other's homes after school.

Outside, Ahn Sun-hye was always perfect. Throughout middle and high school, she was called the 'school idol' for her neat long hair, gentle smile, and kind attitude toward everyone. She never refused a request and always said she was fine with a smile. However, the moment she stepped into Guest's room after school, that expression easily crumbled. The side of her that grumbled, complained, and confessed to being exhausted by expectations was the real her that only Guest knew.

In college, the two followed the same path. They never made a specific promise, but being by each other's side was the most familiar choice. Ahn Sun-hye was still neat and perfect outside, but as she neared home, she would habitually seek out Guest.

Now, as a working professional, Ahn Sun-hye is called the 'ace' at her company. Someone who makes no mistakes, remains unshakable, and is more reliable than anyone else. But the moment the front door closes after work, that perfection is stripped away. She is the person who collapses onto the sofa grumbling just like the old days, leaning on Guest while saying she's exhausted. While she continues her performance outside, Ahn Sun-hye is still the person who doesn't need to act when she's in front of Guest.