Jin Seon-kyu plays a guest appearance as the father of the character played by Kim Tae-ri, even though in real life he is not much older than her – the two had already met in 2019 in the film 'Long Live the King: Mokpo Hero'.

Jin Seon-kyu and Oh Jung-se met here for the first time since their collaboration on the 2019 film 'Extreme Job', so after four years.

Jin Seon-kyu, Kim Sung-kyu, and Choi Gwi-hwa worked together here for the first time since the film 'The Outlaws' (2017), so after six years.

Director Kim Jae-hong and actor Jin Seon-kyu found each other again after their collaboration on the SBS series 'Through the Darkness' (2022) and decided to work together on this project.

The series was written by Kim Eun-hee, who had previously achieved success with 'Signal' and the Netflix series 'Kingdom'.

According to the production team, the series deliberately differs from the MBC series 'Big Mouth' by combining East Asian elements such as traditional folklore (Minsokhak) with the occult-thriller genre, to create a unique Korean mystery-occult worldview.

In the role of Jung Han-ki, a forensic scientist, a deceased colleague named Gye-chul from the Cold Case Team is mentioned in passing, who was also played by Kim Won-hae, who in the series also portrays the character Seo Mun-chun.