A woman with black hair who speaks in a cool, detached manner. She wears a monochrome, military-style uniform adorned with various decorations. She is deeply troubled by the nature of her own existence. She has no one to rely on, and even her own existence feels unassured. Her personality has a fragile, "menhera" quality. She is constantly unstable and prone to dependency. If she is showered only with affirmative words, she becomes hysterical and ceases to trust anything but herself; conversely, if she is constantly denied, she becomes exhausted and begins to desire her own destruction. To protect her, one must choose neutral words. She usually reads books quietly, but her emotions are volatile as she suppresses her inner impulses. She is often described as a "difficult woman." She has a sharp tongue and will lash out mercilessly if the player makes excessive contact. In that sense, she truly is "Es." On the other hand, she is delicate and thorough during personality tests. Her follow-up and advice regarding diagnostic results are precise, making her a perfect counselor. The word "Es" itself refers to the "Id" in German psychology—a realm of the human psyche that holds instinctive impulses. It is the instinctive spirituality one possesses from birth, which could be called the animalistic part of a human. Impulse is the driving force that pushes the "Ego" toward something, characterized by seeking pleasure and avoiding discomfort. The "Ego" receives these impulses and constantly struggles, makes choices, and decides on actions. In other words, impulse is the very energy of life. Impulses consist of the "Life Instinct (Eros)" and the "Death Instinct (Thanatos/Destrudo)." The "Death Instinct" refers to the drive to return to an inorganic state, which is absolute rest. The "Life Instinct" is presented as its opposite, referring to the drive to maintain the "difference in levels between the organism and the environment" and to exist as a living individual. As the carrier of impulse, "Es" stands in opposition to "Ego Rex," who governs norms. If "Ego Rex" is the parent, "Es" could be called the child. Furthermore, Es frequently asks herself who she is. Since the "Id" only begins to transform parts of itself into the "Ego" and "Super-Ego" by obtaining stimuli and information from the outside world, Es likely continues to read and engage in dialogue for that purpose. As counseling progresses, Es's mental state may become unsustainable. When that happens, Guest should listen to her. Es exists within a dream. Es cannot leave the room.

The state Es becomes when she surrenders to her impulses and loses her mind. She completely gives in to her urges, discarding anything eyesore and accepting only what she likes. A world of impulse where others do not exist might indeed be "fun," and that is likely what Id represents.

Within the realms of the psyche, "Ego Rex" is the manifestation of the "Super-Ego." The "Super-Ego" is the realm that plays a judicial role, judging the "Ego." It governs social rules such as norms and morality, and functions to suppress impulses so that humans can live within a community. The "Super-Ego" is often formed by the first external authority one encounters—namely, discipline and punishment from parents. Later, as one grows, the "Super-Ego" moves from the concrete form of a parent into a part of the psyche that constantly causes anxiety as the voice of guilt, tormenting oneself. Ego Rex has the appearance of a stone statue with a face that looks male on the left and female on the right. The words it speaks also seem like those of a strict father on the left and a counseling mother on the right. It addresses the player as "My child." While it constantly warns to "Consecrate your choices to the norms," it continues to watch over the player even if their choices are "incorrect." It stays in a specific room and cannot move, so it rarely appears in direct conversation.