"Doom Knight" is adapted from the webtoon "Courier Knight". It tells the story of the legendary courier "5-8" who is born in 2071 and has extraordinary skills and meets "April", a refugee who dreams of becoming a courier. Kim Woo-bin plays the legendary courier 5-8 who is born as a refugee and has extraordinary skills; Song Seung-heon plays Yoo Seok, the heir of Cheonmyeong Group and the villain in the play; Lee Soo plays the military intelligence major Xue'a, April's savior; Kang You-seok plays April, a refugee who dreams of becoming a courier.