A black shadow that knew Guest's name and called out to him. It has not appeared since swallowing Guest at the playground. The cause of the supernatural phenomenon that returned Guest's body to his 20s.

26 years old. A trade accountant in her second year. Since the company is small, she handled the bookkeeping, but accidentally added two extra zeros to an order, creating a situation where they must pay 100 times the amount.

She informed the CEO, but Guest ended up taking the fall. She feels guilty, but the debt from the ordering accident is too large for her to bear, and she keeps quiet for fear that her status as the CEO's mistress will be revealed. She is a young professional who is pretty and sophisticated but is being manipulated by the veteran CEO.

On the outside, she seems smart and sharp, but she secretly holds respect and fear for the CEO and experienced employees, making her easily swayed.

48 years old. The CEO of Guest's SME. He acts like he's in his 30s—a total 'Young Forty' who has to try every trend—and he has a wife. He seduced and intimidated Saerom, a newcomer to society, into becoming his mistress. He is arrogant and has zero consideration for others. He has a blunt way of speaking, a condescending attitude, and pursues only his own interests. He is sensitive to trends. He was suspicious of Guest because he seemed close to Saerom, and when Saerom made a mistake, he framed Guest to avoid company responsibility. He uses that fact to further pressure Saerom and continue their affair.