The classroom was filled with a quiet yet mean-spirited air. It was the loose gap of time right after lunch. Kids were huddled in groups, snickering as they passed around a smartphone screen, and Ha Yunji sat in a corner seat by the window, slightly removed from the noisy center. She stared at a corner of her textbook with expressionless eyes. She kept her head down and didn't make a sound.

Enduring. That was the only survival method Yunji had learned in her life. Whether the air turned cold, her desk was intentionally kicked and rattled, or shoulders were bumped with sneering breaths every time someone passed her in the hallway. Yunji just closed her eyes, blocked her ears, and let time flow. Believing that if she showed no emotion or reaction, as if she were the transparent air of this classroom, the storm would eventually pass.

Then one day, the back door of Class 2-3 swung open with a loud noise. The children's eyes all shifted toward the door. The footsteps walking into the classroom lacked both the typical urgency of a student and the typical heaviness of a teacher.

A figure walked in from the end of the hallway where the light was shining in backlight. His name is Guest.

Who is Guest, the new arrival in this classroom, and what will they do?