Following the release of the comedy drama Mundasupatti (2014), Ramkumar was keen to do a serious film to avoid being type-cast.
Ramkumar was inspired to write a film on a psycho killer after reading a news story about Alexander Spesivtsev, a russian serial-killer, who targeted children and young women, tortured and kill them.
Ramkumar spent close to 2 years writing the screenplay for Ratchasan, adapting the real-life incidents into a story that happens in Chennai.
Ramkumar struggled to find an actor to play the lead role of a 40-year-old man with a child, and despite working the child out of the script as a result, he still found it difficult to cast the lead.
In April 2017, actor Jai signed the project titled Ratchasan, which was set to be produced by C. V. Kumar of Thirukumaran Entertainment.
However, soon after the launch, the actor dropped out of the project, and CV Kumar took the title of Ratchasan with him.
Ramkumar chose to make the film with producer Dilli Babu and starring Vishnu and Amala Paul in the lead roles in July 2017.
The filmmaker-who-reluctantly-becomes-a-cop angle was incorporated after Vishnu came into the film.
This became the second film collaboration between Vishnu and director Ram kumar. They previously worked on Mundasupaati.
Throughout the production stage, the second Ramkumar film was briefly known as Cinderella and then as Minmini, as the title Ratchasan was with CV Kumar
The team eventually managed to amicably convince Kumar to offer them the title of Ratchasan, which was later stylised to Ratsasan.
The girl Sanjana, who gets kidnapped has a twin. Sanjana is seen wearing bindi and a gold necklace whereas her twin has no bindi & a blue necklace. These are not made evident in the film.
The producers that Vishnu meets seeking a directorial debut demand commercial, horror, drama content respectively. These producers have a commercial, horror & drama movie posters behind in their rooms
The scene where a teacher harasses the girl is cross-cut with a speech on woman empowerment. Simultaneously, the magician (easter egg) keeps searching for chances to kill the girls.
The talk about women empowerment superbly camouflages this easter egg.
Vishnu Vishal's character gifts a piano to Ammu. She is later killer by a psycho who loves playing the piano.
The radio station is where the main lead finds an evidence about the psycho. The benches of the station are painted like a piano with black and red keys, instead of black and white keys.
Ratchasan was ranked at 2 in the IMDb Top Indian Movies of the year 2018.
The magician is revealed to be the psycho. Earlier, when the magician is introduced, she is seen performing magic tricks, which symbolizes killing. This again is an easter egg.
Sanjana is kidnapped and trapped in a torture chamber by Christopher. In the torture chamber, one can see the uniform of Amudha and birthday dress of Ammu who were tortured to death prior to her.
Christopher's character is shown to be having 5 fingers in the flashback, but he has 6. This may be regarded as a goof, but the character, who narrates the flashback, later acknowledges the 6th finger
The title Ratsasan is depicted in a piano font with a housefly on it, but during Intermission, the title card shows the same fonts to be having blood on it which symbolically represents Ammu's murder.
Samyuktha's corpse was found on September 1, 2016 according to the news article, but when Vishnu addresses the time line on a board, he writes as October 20, 2016. This's a goof up.
The film takes place in 2016 but in a scene, the digital clock reads 23.01.2018.
Ammu Abirami's character gets killed in the film. Her character also gets killed in Thuppaakki Munai and Asuran.
Ratchsan's album by Ghibran M features 41 tracks for a duration of nearly 54 minutes. Out of those, only four are featured as songs.
The lyrics for the film's album were written by Umadevi, Ramkumar, Ratnakumar and GKB.
Saravannan, who played the killer Christopher, had to lose weight, sport heavy prosthetics, and shave his head to look the part.
In addition, Saravannan also worked to master the body language of an aged Anglo-Indian woman and a progeria patient for playing the dual role of Mary Fernandez and his progeria-affected son.
Ratchasan was one of the rare films to complete a 100 day-run in many cities in TN.
The film went on to gross 20 crores and became one of Vishnu Vishal's highest grossing movies.
