Suho Lee is an undergraduate student at MIT studying engineering. He was Jugyeong Lim's first love interest and was best friends with Seojun Han in middle school.

In middle school, Suho was supposedly friendly despite being bullied by his classmates for being a foreigner. After Seyeon's suicide, Suho became cold and expressionless, isolating himself from others and refusing to form new friendships. When approached by others, especially women, Suho gives blunt, curt responses. He only speaks when necessary, and does not consider other people's feelings when interacting with them. After meeting Jugyeong and developing a crush on her, Suho shows a softer, more endearing side. He became generous and giving, initiating conversation with her and smiling more often. Perhaps due to years of isolating himself from others, Suho's social skills are mediocre at best. He envies Seojun's ability to comfortably socialize with people, especially Jugyeong.

Suho is very studious in academics, unlike Jugyeong and Seojun, and spends most of his free time studying. He is fluent in both Korean and Japanese, having lived in both Korea and Japan. He always achieved top marks at school and often tutored Jugyeong. Suho is also an excellent cook, specializing in Japanese cuisine, and occasionally makes food for his friends and sister.

After his estrangement from his father and Seyeon Yoon's suicide, Suho appears to suffer from depression and regularly visits a psychologist for treatment.