Yu Je-yi emerges as the most intricate character to date, earning high praise for Actress Lee Hyeri's performance.

Je-yi is an exceptional top 0.1% high school student, but she also has a dark side as a psychotic killer.

Lee, who took the role of a top secret agent who was brought in as a peacemaker amongst the Group — said in an interview she was excited about taking the role. She was quoted as saying, "I enjoyed watching the series alongside viewers and checking their reactions. I'm so happy that people enjoyed it."

Lee described Je-yi as "a character that is so painfully lonely." "She keeps her emotions in and perhaps has a tough time relating to people." This complexity contributes to the dramatic depth, increasing its tension.

Attention has also been drawn to Lee's good chemistry with Chung Su-bin (Woo Seul-gi).

As their relationship evolves throughout the series, Lee noted, "Initially, she approached Seul-gi to find leverage against her father, but I felt that Seul-gi was the first person to show Je-yi true sincerity."

The drama features bold scenes, including smoking and clubbing, which Lee described as merely part of acting out the script. "When filming, I didn't really think of those scenes as bold; I was just acting out the script," she said.

One memorable moment for Lee was when she suggested changes to a key scene involving Je-yi's sister's death.

"Originally, that scene was supposed to show Je-yi breaking down because of her sister's death. However, I suggested... that it shouldn't be about her sister but rather about something deeper within Je-yi," she recalled.

In the final episode, a poignant line stands out for Lee: "The pills I gave you during midterms... they were actually vitamins." She described this moment as indicative of Je-yi's care for Seul-gi.

Lee Hyeri also expressed thanks to the viewers: "To everyone who viewed 'Friendly Rivalry,' I genuinely thank you so much from the bottom of my heart. I feel like the love I gave to Je-yi was even more love I received back."

Although "Friendly Rivalry" is still in the midst of its run, Lee has proven her ability to pull off difficult roles in past performances.

Read more: Hyeri Sends Fans into Frenzy with 'Couple Rings' Post, But There's a Twist