"I've never thought it'd be easy, but if you try hard, you can definitely do it." - Park Sae Roy

Itaewon Class OST Part. 3 ""Diamond"" is a powerful song that expresses the stories of a young man, Park Sae Roy (Park Seo Joon), who does not give up on his beliefs even after losing everything.

In the drama, Park Sae Roy is not only expelled when he could not kneel despite facing injustice but also convicted of attempted murder after attacking his enemy who killed his father. However, he does not feel any resentment or regret for his actions that he chose. That is Park Sae Roy's values and beliefs. Park Sae Roy is a diamond that becomes even brighter after going through hardships.

The original writer of the webtoon ""Itaewon Class"" and the scriptwriter of this drama, Jo Gwang Jin, wrote the lyrics for the song ""Diamond"", which perfectly expresses the iconic character, Park Sae Roy, whom is not swayed by anyone else and is solely focused on his own beliefs and values. Additionally, Ha Hyun Woo's solid and powerful vocals give off a certain tension, flawlessly conveying Park Sae Roy's will to fight for his beliefs in a tough world, giving the viewers and listeners a sweet cathartic release.