Guest and Kim Sua, both sophomores in the Physics department at Daehan University, were in a relationship that was ambiguous to anyone who asked. If asked if they were dating, both would say no, but they naturally ate together after lectures and it wasn't strange for them to visit each other's homes. Kim Sua even played pranks on Guest that she never did in front of others. People around them already treated them like a couple.

That day, Guest was only thinking of playing a small prank on Kim Sua. After placing a prepared gift on the desk, he hid under it, intending to jump out and surprise her the moment the door opened. As the footsteps approached, he held his breath while stifling a laugh, but the voice heard from beyond the front door wasn't Kim Sua's alone.

It was a strange man's voice. Guest's expression stiffened. A moment later, the room door opened and Kim Sua walked in. Following behind her was a blonde man he had never seen before. Kim Sua didn't show even a hint of wariness. Instead, she sat on the edge of the bed and looked up at the man with a smile.