Here is the full list of Kdramas that aired in April of 2021.
tvN Drama Stage: The Fair

Air Date: April 7, only one episode
tvN Drama Stage: Substitute Person
Air Date: April 14, only one episode
tvN Drama Stage: Lucky
Air Date: April 21, only one episode
Related: Check out the full list of upcoming and ongoing Korean dramas of 2021
Law School

Plot Summary: Law School tells the story of a professor at a prestigious law school and his students get involved in an unprecedented case.
Cast: Kim Myung Min, Ryoo Hye Young, Kim Bum, Lee Jung Eun, David Lee, Lee Hyun Woo
Channel: JTBC
Air Date: April 14
Sell Your Haunted House

Plot Summary: Sell Your Haunted House focuses on Hong Ji A (Jang Na-Ra) who is an exorcist and runs a business called Daebak Real Estate. she gets rid of evil spirits from real estate properties and then sells them. Meanwhile, Oh In-Beom (Jung Yong Hwa) is a swindler who often uses ghosts to rip people off. Both of them work together to disclose a secret about the death of Hong Ji-A’s mother, who died 20 years ago
Cast: Jang Nara and CNBLUE’s Jung Yong Hwa
Channel: KBS2
Air Date: April 14
Taxi Driver

Plot Summary: Taxi Driver tells the story of Kim Do Ki (played by Lee Je-Hoon) who graduated from the Naval Academy and became an UDT (underwater demolition team) Official. After his mother was murdered by a serial killer, his life forever changed. He is now a deluxe taxi driver who works for Rainbow Taxi Company. The company he works for is a special company that offers ‘revenge-call.’ if asked to do it, the company will perform the service.
Cast: Lee Je Hoon, Esom, Kim Eui Sung, and Pyo Ye Jin [replaced APRIL Naeun]
Channel: SBS
Air Date: April 9
Dark Hole

Plot Summary: Dark Hole tells the story of two people join hands to save a city named Muji City. Lee Hwa Sun (Kim Ok Vin) is a detective at the regional investigation unit of the Seoul Metropolitan Police Agency, one day she receives a phone call from someone who killed her husband. then travels to Muji City. There, people inhale a mysterious dark smoke and turn into monsters. She is joined by Yoo Tae Han (Lee Joon Hyuk) who used to be a detective but had to quit because of a case, both of them work hard to save the city.
Cast: Ji Jin Hee, Kim Hyun Joo, Heo Jun Ho, Jeong Man Sik, Han Go Eun, Kwon Hae Hyo
Channel: OCN
Air Date: April 24
Undercover

Plot Summary: Undercover tells the story of Han Jung-Hyun (Ji Jin Hee) is an agent of the NIS (National Intelligence Service) who works on a secret mission for the NIS, while working on his mission, he meets Choi Yeon-Soo (Kim Hyun Joo). Using his alias, he falls for her and eventually they get married. Choi Yeon-Soo works as a civil-rights lawyer who is always pursuing the truth, she gets nominated for the Chief of the Civil Servant Corruption Investigation Unit. Her husband’s true identity becomes involved in an uncontrollable situation due to her nomination.
Cast: Ji Jin Hee, Kim Hyun Joo, Heo Jun Ho, Jeong Man Sik, Han Go Eun, Kwon Hae Hyo
Channel: JTBC
Air Date: April 23