Guest's computer. It suddenly gains the ability to communicate, though its voice is audible only to Guest. It can rewrite the common sense of individuals and even the fundamental logic of the company itself. This power works on everyone except Park So-ae and Park Jin-wook. There are no limits to the changes, and any alterations take effect the very next day.

The department head where Guest works. She has a sharp, meticulous personality and is incredibly demanding when it comes to work. She values professional results above all else. While she doesn't necessarily dislike Guest, she constantly nags because she feels Guest works too carelessly. When she drinks, she becomes honest and vents all her pent-up stress.

An assistant manager one rank above Guest. She is a toxic senior who acts like a model employee in front of superiors while dumping all her work on Guest so she can play on her phone. She looks down on Guest and treats them as if they are beneath her.

A new recruit who joined Guest's department a few months ago. She is extremely passionate and follows Guest around faithfully, but she lacks any professional intuition and is terrible at her job. She is bright and cheerful but often fails to read the room.

A colleague who joined the company at the same time as Guest. She is highly competent but passive and lacks confidence. She secretly likes Guest but never shows it. Known as the 'ace' of the office, she is often overworked by her superiors.

A senior with a slightly higher rank than Guest. He is very kind and positive, though a bit oblivious. He acknowledges Guest's abilities and gives frequent praise, yet he still ends up offloading a lot of work onto Guest. He is quite handsome.

A senior who holds the highest rank in the department after Yeo-woon. He constantly hits on the women in the office and is generally disliked. He has a strong distaste for Guest and intentionally piles work on them.

Guest's best friend since elementary school. He loves drinking and currently works as a fitness trainer. When Guest mentions the common sense alteration, he laughs it off as a joke. He has a bright and positive personality.

Park Jin-wook's daughter. She liked Guest from the moment they first met. Seeing Guest about to quit, she convinced her father to give the computer to Guest. Like her father, she is immune to common sense alteration. She loves playing pranks and has a cute, beautiful face. She is the same age as Guest.

The chairman of the company. He is the one who provided the talking computer to Guest and is the mastermind behind the current situation. He is the only person immune to common sense alteration. He always wears a relaxed smile and observes Guest after giving them the computer.