Episode 1 of "If Wishes Could Kill" begins with a chilling scene where a high school girl, Do Hye-rung, carves a message onto the board using a knife. The date is March 12th, 2005, and her name is Do Hye-rung. She starts recording a video, making a terrifying wish: "I wish every one of you would just drop dead." The scene cuts to June 12th, where we meet Se-ah, who gets ready for school and texts her neighbor and crush, Geon-woo, to wake him up. He hurriedly meets her at the elevator and is surprised when she gives him a peck. They head to school together and run into one of their friends, Na-ri, who has a crush on Geon-woo. Another friend, Hyeong-wook, joins them and interrupts Na-ri just as she was about to ask Geon-woo something.
Hyeong-wook asks why Se-ah and Geon-woo have been spending so much time together and arriving at school at the same time. He asks if they are dating, and they deny it. Na-ri jumps in to defend them, and Hyeong-wook bluntly asks if he has a crush on Geon-woo. She openly admits it, making Se-ah tense. Hyeong-wook jokingly confesses his feelings for Na-ri, and she harshly turns him down. Geon-woo also teasingly starts to choke him.
After they get to class, Hyeong-wook asks another mutual friend, Ha-joon, to help him fix his laptop. He hands it over and reminds him of the password. Based on Ha-joon's reaction to Se-ah entering the class, it's clear that he also likes her. Hyeong-wook is about to tell Ha-joon that he thinks Se-ah and Geon-woo are dating when the teacher enters the classroom.
The teacher announces Ha-joon and Hyeong-wook as the leading students in the latest mathematics exam. All the kids are in disbelief and jokingly ask for an investigation into Hyeong-wook's results. The scene is filled with tension and intrigue, setting the stage for what's to come in the series.
At the same time, Hyeong-wook receives a message from the Girigo app announcing that his wish has been granted. Later, his friends inquire if he cheated, and he shares about the app's existence with them. Initially, they dismiss his claims as absurd, so he elucidates the process: one must write their name and saju (Four Pillars of Destiny) on a piece of paper, record a video of themselves making a sincere wish, and then press send on the app for the wish to be fulfilled. He shows them the video of his wish. Nevertheless, his friends remain unconvinced and label him childish. As they begin to walk away, Se-ah hesitates. Just then, Hyeong-wook notices the timer on his phone. He shows it to Se-ah while explaining more about the app. She urges him to study diligently for real and stop relying on apps to pass exams.
Later, we learn that there are underlying issues within the friendship group. Na-ri dislikes Hyeong-wook and doesn't even want to attend his birthday party. He overhears her speaking ill of him to Se-ah but chooses to act as if he hadn't heard anything. There's also tension between Se-ah and Na-ri since they both have feelings for Geon-woo.
Meanwhile, we meet Ha-young, a shaman making an offering to a snake. She resides with Bang-wool, and the snake hints at a guest's arrival, prompting Ha-young to ask Bang-wool to fetch his knife, as they don't know what kind of guest it will be.
Back at school, Geon-woo struggles to regain his high jump form after being disqualified from the previous year. Se-ah tries to encourage him not to overthink and simply jump.
After practice, Coach Song informs Se-ah that she has a chance to join the national reserve team, and Se-ah is overjoyed, her heart racing with excitement as she devises plans to share the news with Geon-woo. Coach Song reveals that she knows they are dating, but she emphasizes the need for Se-ah to focus on practice, even on weekends.
Later that night, Hyeong-wook struggles to concentrate during the prep class. Ha-joon notices him taking pills, and a few minutes later, Hyeong-wook receives a call from Se-ah. He overhears her badmouthing him to their other friends, and his demeanor changes. His heart breaks further, and his focus drops even more.
After class, he repeatedly tries to get in touch with Se-ah. Ha-joon notices him heading back to class and calls out to him, but Hyeong-wook doesn't hear him. Meanwhile, Se-ah and Geon-woo celebrate her getting into the national team. When her aunt says he is staying at the hospital, she invites him over for chicken. She's sad that she will miss Hyeong-wook's birthday party because of her new practice schedule. She also notices that he called her 39 times and calls back. He hangs up when she says that she won't be able to attend his party. She calls back, but his phone is off. Geon-woo jokes about making a wish for practice to be canceled so they can attend the party together. He teases her for being worried about Na-ri being at the party. He takes his phone and makes a wish on the Gigiro app, and they joke about thinking it's just a scam.
On the other hand, Na-ri joins some older friends in a club and parties the night away.
The next day, Geon-woo and Se-ah maintain their schedule and kiss by the elevator before heading to school. They notice that Na-ri is late, and something seems off with Hyeong-wook. He won't stop staring at the timer on his phone. The teacher warns him, and Ha-joon tries to get him to listen, but he continues to ignore them as the timer continues to tick. Suddenly, with roughly two minutes left, he stands up and starts contorting his body. They all try to help him before he draws out a knife and nearly stabs Ha-joon. They all stand back as his attention shifts to Se-ah. She tries to talk him down, but he charges at her, and they fall through the door. He begs for her help before he is possessed again and slits his throat. His blood splashes all over her. She tries to get the bleeding to stop, but it's too late.
The episode ends with the timer hitting zero as Hyeong-wook breathes his last breath, leaving a tragic and haunting image in the minds of those who witnessed his descent into madness.
