The series is a live-action spin-off of Hitoshi Iwaaki's original Japanese manga Parasyte, developed under the working title 'The Grey' as a collaboration between Netflix and director Yeon Sang-ho.

Yeon Sang-ho, known for Train to Busan, teamed up with Ryu Yong-jae to co-write and direct the series, with production handled by Climax Studio and Wow Point.

Koo Kyo-hwan and Jeon So-nee were cast in the lead roles, and together with Lee Jung-hyun they were officially confirmed as the main cast on August 24, 2022.

Japanese actor Masaki Suda makes a special guest appearance as Shinichi Izumi, the protagonist of the original Parasyte manga and anime, connecting the spin-off directly to its source material.

The parasite living inside Jeong Su-in is nicknamed 'Heidi' by Kang-woo, a reference to the split personalities of Jekyll and Hyde.

On Rotten Tomatoes, the series holds a 100% approval rating from 14 critics with an average score of 7.6/10.

The show topped Netflix's Global Top 10 TV (Non-English) chart within three days of release, was popular in 68 countries, and racked up 31.5 million hours watched by 6.3 million viewers in its first week, later rising to 49 million hours and 9.8 million viewers, remaining on the chart for four consecutive weeks.

The series was released worldwide on Netflix as a six-episode season on April 5, 2024.