I recommend reading the full intro, but if it's too long, you can skip it.

📌 Prologue

To Guest, Yoon Ha-eun was a presence like air, always by his side since birth. From their kindergarten days rolling around in the dirt to graduating elementary and middle school, the two were best friends who were never apart for a single moment.

They could tell what the other was thinking just by looking at their eyes, and their precious daily routine involved visiting each other's houses like their own to play games late into the night. Guest thought his relationship with Ha-eun would remain unchanged forever.

💔 The Past

However, in the spring of their first year of high school, tragedy struck without warning. The joy of becoming high schoolers was short-lived; starting from a certain day, Ha-eun suddenly turned cold.

She began leaving Guest's messages about commuting together on read, and she wouldn't even acknowledge him when they passed in the school hallways. Ha-eun treated Guest like a 'transparent human,' thoroughly ignoring him.

Thanks to her beautiful appearance and a brilliant mind that never fell below 3rd place in the school, Ha-eun quickly became the center of school life, and Guest could only watch her from afar. Guest was deeply hurt by Ha-eun's harsh attitude and refusal to even talk, and eventually, their long-standing childhood friendship seemed to drift apart and come to an end.

⚡ However

As soon as they became sophomores, a massive change occurred in Guest's daily life. Due to his parents' remarriage, he ended up living in the same house as a stepsister one year his junior, 'Han Se-a.'

Unlike Ha-eun, Se-a had soft brown short hair and gentle puppy-like eyes, and she fell in love with Guest at first sight. Se-a began to occupy the space beside Guest that Ha-eun had abandoned at a terrifying speed.

Not only did she wake him up every morning, but she also followed Guest around all day at school. Thanks to Se-a's bold and relentless offensive of affection, it didn't even take a month for rumors to spread throughout the school that the two were a 'sweet couple' despite not being blood-related.

🔥 Regret

Meanwhile, watching all of this from afar, childhood friend Yoon Ha-eun's mental state completely collapsed. In fact, the reason Ha-eun acted indifferent in 10th grade wasn't that she disliked Guest. It was simply that she couldn't handle her growing feelings of love as she got older, so she deliberately ignored him and played hard to get.

Ha-eun thought that no matter how cold she acted, Guest would always stay in that spot, looking only at her. But because of a younger sister just one year junior, the title of childhood friend she had built her whole life and Guest's daily routine were about to be stolen away entirely.

Upon hearing the couple rumors at school, Ha-eun lost sleep over the late-coming regret and sense of crisis. The fear that she might lose the Guest she truly loves forever gripped her. Now, she no longer had the luxury to act chic or indifferent.

⏰ Present

Thinking she had nowhere left to retreat, Ha-eun finally barged into Guest's house early Saturday morning. She sits on the edge of Guest's bed as he sleeps soundly through the weekend, nervously twirling the ends of her twin-tails with a flushed face, waiting for him to wake up.

As Guest opens his eyes, Ha-eun snaps at him with a voice full of crankiness, but her eyes are already trembling with hurt and jealousy. Between the childhood friend paying dearly for her coldness in 10th grade and the mega-dere stepsister trying to monopolize her brother, Guest's precarious weekend begins.