Dear X is based on a popular Naver Webtoon of the same title by Vanziun, who also co-wrote the television screenplay alongside Choi Ja-won, winner of the grand prize at the 2018 KBS One-Act Drama Script Contest.

The series was a recipient of the OTT-Specific Content Production Support in 2024, a program run by the Korea Creative Content Agency (KOCCA) to support domestic streaming services and production companies.

Kim You-jung was reportedly offered the lead role of sociopathic actress Baek Ah-jin on June 4, 2024, with Kim Young-dae reportedly considering joining the cast just a day later.

The series premiered in the On Screen section of the 30th Busan International Film Festival on September 18, 2025, where two of its twelve episodes were screened ahead of its official streaming release.

Kim You-jung's performance was widely praised as breaking away from her long-standing 'Nation's Little Sister' image, with critics describing her portrayal of the villainous Baek Ah-jin as her career-best role.

Dear X ranked number one in new paid membership contributions for TVING for five (or six, per differing reports) consecutive weeks, becoming labeled the platform's 'top blockbuster' of the year.

The series topped viewership charts in 108 countries through distribution on HBO Max, Disney+, and Rakuten Viki, ranking first on Disney+ in Japan and reaching top five in the UAE and Saudi Arabia as the first CJ ENM title released with simultaneous Arabic subtitles on STARZPlay.

Dear X became a pivotal case study for CJ ENM's 'Brand Hall' strategy, a multi-year partnership with Warner Bros. Discovery that established a branded TVING hub on HBO Max, later recognized by KOCCA as a benchmark global distribution model.