O Kadhal Kanmani

In early 2014, Mani Ratnam first approached Telugu actor Ram Charan to be a part of the film, but he felt the lead role would not work for him.[10] In August 2014, Madras Talkies had confirmed that Dulquer Salmaan would play the lead role in their forthcoming production and it was reported that Mani Ratnam's regular collaborator, composer A. R. Rahman would also work on the film.[11][12] Vairamuthu renewed his collaboration with Mani Ratnam and A. R. Rahman to write song lyrics, and stated that the director had told him the film's plot concisely within three minutes and described it as a "beautiful love story" about "two characters and their love and mindset".[13] P. C. Sreeram joined the team later in the month, collaborating with the director after Alaipayuthey (2000).[14] During the making of the film, the cinematographer hinted that the film has contents on the lines of Ratnam's Alaipayuthey (2000), and that it was also loosely based on a real life incident.[15] In October 2014, the film was revealed to have a working title of OK Kanmani.[16][17]

Mani Ratnam revealed that he had the fascination for making a film on the gaming culture before Kadal, and set the story in Mumbai as it was India's gaming hub and a place where a live-in relationship can happen more naturally than in South India.[18] He revealed it was an urban love story, and added that the Mumbai setting was also justified as it dealt with people away from home who become independent of the rules and regulations of a family.[19] The film was earlier wrongly reported to be bilingual in both Tamil and Malayalam; it was made only in Tamil.[20]

In a press conference at Taj Coromandel in Chennai, Ratnam said that the film is a contemporary take on the new generation, their attitudes and their values.[5] Through the film, Ratnam wanted to portray the change that takes place every five or six years when a new generation comes in with a different set of values.[5]

The female lead role was initially offered to Alia Bhatt, who opted not to work in a regional film, while Pooja Hegde also refused the offer, citing her commitment to Ashutosh Gowariker's Mohenjodaro (2016), which prevented her from working on other films.[21] Parvathy Thiruvothu was also considered, before Nithya Menen was selected.[22] Dulquer and Nithya worked together on O Kadhal Kanmani alongside their commitments in Jenuse Mohamed's Malayalam film 100 Days of Love, which eventually released a month before Mani Ratnam's film.[23] The director revealed he first met Dulquer at the audio release function of Vaayai Moodi Pesavum (2014) and felt that he was the right choice to play the character Aadi, although he hadn't seen any of the actor's films. Ratnam had only previously seen Nithya Menen's 180 (2011) and Urumi (2011), where she had played small roles but was impressed.[5] Ratnam was quoted saying, "I found something alive about her, something real and perfectly beautiful about her. Nithya carries an individuality and is not just a glamorous girl. Like her character in the film, Tara, she has a mind of her own."[5]

Prakash Raj accepted to play a role in the film in September 2014 and expressed his excitement at being offered a unique character.[24] Leela Samson, a Bharathanatyam dancer and author, was selected to make her acting debut and portray a retired Carnatic singer in the film, appearing as Prakash Raj's wife.[25] Television anchor Ramya Subramanian was also picked to play Dulquer's friend in the film, and it became her first full-fledged acting role.[26] The rest of the cast consisted of Mani Ratnam's assistant directors Sivakumar Ananth and Chandrika Chandran, while his friends Rama Ramasamy, Prabhu Lakshman and the former manager of Sify, John Devasahayam, were given other roles. Actress Kanika shot for a day in Chennai, to portray a small role in the film as did architect B. V. Doshi.[27] A number of rookie actors, who later went onto feature in larger projects, including Arav, Ashwin Kumar Lakshmikanthan, Ciby Bhuvana Chandran and Pavithra Lakshmi made appearances as colleagues of Dulquer's character.[28][29][30]

Principal photography began from 6 October 2014 with scenes featuring Dulquer Salmaan and Nithya Menen being filmed.[31] Menen revealed that the film would be shot in a short span of time and her portions would be completed by December 2014, while the team swiftly shot scenes at locations in and around Chennai, including near a bank in Parry's Corner. The last leg of filming, started in Mumbai in November 2014 with the shooting lasting for a week.[32] The team shot scenes at Indian Institute of Management Ahmedabad and CEPT University during December 2014, with renowned Indian architect B. V. Doshi filming for a guest appearance as Nithya's mentor. The team subsequently moved back to film further outdoor sequences in Mumbai, later that month.[33][34] Following the schedule, P. C. Sreeram revealed that the film was practically complete and that the film would aim to release in early 2015.[35]

The game animations for the film were handled by Studio Dreamcatcher, who worked on two versions of a fictional game called Mumbai 2.0, which Dulquer's character develops in the film. A 2D prototype and a 3D 2.0 version were created for the film, while the team also took care of the animation sequences for the end credit segments. The company also took care of character designs, story board and animatics of the lead characters Dulquer, Nithya and John for the 3D sequences.[36] The 2D animated opening title sequence for the film was handled by Mumbai-based animation studio Plexus.[37] The film's title was changed in February 2015 from OK Kanmani to O Kadhal Kanmani in an attempt to gain an entertainment tax exemption in Tamil Nadu, through the use of a pure Tamil title.[38]

O Kadhal Kanmani received positive reviews from critics upon release, with International Business Times India calling it "the director's best in recent years" in their initial review round-up.[8] Baradwaj Rangan of The Hindu wrote, "O Kadhal Kanmani is something of a greatest-hits package of Mani Ratnam", while also singling out Nithya Menen's performance for praise. He added "we’re all going to have our favourite scenes with her" and "if Mani Ratnam keeps employing actors like her, he may not need to write those zingers anymore."[53] Anupama Subramanian of Deccan Chronicle wrote, "After a couple of lackluster flicks, master story teller Mani Ratnam is back with a bang with a feel good complete romantic movie O Kadhal Kanmani. There are a few overall glitches, nevertheless, watch OKK for its fresh approach and feel-good entertainment it offers." She awarded the film 3 stars out of 5.[54] Reviewing for Firstpost, Latha Srinivasan stated, "O Kadhal Kanmani celebrates romance, an emotion that is as old as creation itself (remember Adam and Eve?). Mani Ratnam is back, with a 21st century love story that will charm you."[55] Udhav Naig of The Hindu said "Ratnam has made a film that will not only resonate with audiences across India but has also truly retained the Tamil flavor".[56] Naig called it is as one of those films in which everything seems to have come together: music, acting, editing and the cinematography.[56] The critical review board of Behindwoods gave the film 3.25 stars out of 5 stating, "Okay, moral of the story – One fine morning, Mani Ratnam got up and decided to make something special for all young people out there. He then makes OK Kanmani, and in style".[57]

Critics based at Sify stated, "The premise is simple, the story is focused. Technically OK Kanmani is superior as both AR Rahman and PC Sreeram have given their career best work for Mani Ratnam as the master craftsman himself is in tremendous form. O Kadhal Kanmani is definitely above a notch compared to the mediocre cinema we have been subjected to lately."[58] Sudhish Kamath wrote, "OK Kanmani is unfortunately that Uncle who makes you believe that marriage is the answer to your conflict of living in without any expectations from each other."[59] Haricharan Pudipeddi for Hindustan Times said that the film is a refreshing take on romance and relationship. This is his best work in years and this magical spell won't be forgotten easily. By throwing the spotlight on modern India's idea of romance, Ratnam has also succeeded in making us root for an older couple madly in love in O Kadhal Kanmani."[60] Karthik Keramalu of IBN Live stated that the film is a love letter to the audience. He went on to call the film as, 'Mani Ratnam's timely reflection of our society' which mustn't be missed.[61] He rated the film 5 out of 5.[61] R. S. Prakash of Bangalore Mirror wrote, "Mani delves into the plot of live-in relationship, but he has chosen not to go overboard, given the sensitivity of the subject, especially in his part of the world. The screenplay, though a bit implausible at places, flows steadily, carrying the touches of the master filmmaker."[62] Writing for The Times of India M. Suganth said, "The filmmaker shows that his touch is intact and he can still make a romance come alive on screen." The film was rated 3.5 out of 5 by him.[63] Indo-Asian News Service stated, "By throwing the spotlight on modern India’s idea of romance, Ratnam has also succeeded in making us root for an older couple madly in love in “O Kadhal Kanmani”."[64] S. Saraswathi of Rediff.com gave the film 3.5 out of 5 stars claiming that it has, "director's trademark, unique narrative style, realistic characters, and excellent performances coupled with great music and stunning visuals".[65]

Madras Talkies made the film at a cost of ₹6 crores and upon release, it immediately became a profitable venture for producers and distributors, amassing ₹14.73 crore from its Tamil and Telugu dubbed version worldwide, within four days of release.[66][67] In Tamil Nadu, O Kadhal Kanmani grossed nearly ₹6.30 cr in its first three days, opening at second place behind Kanchana 2 and experienced particular success in multiplexes as expected.[68]

O Kadhal Kanmani also did "exceptional business" overseas, with theatrical rights sold worldwide for ₹2 crore. The venture managed to gross approximately $714, 000 (₹4.42 crore) from the US market alone, becoming one of the most successful Tamil films of all time in the US, as its acquisition price was very low compared to its business.[69][70] During the opening weekend, the Tamil version of the film grossed ₹2.76 crs in the USA while the Telugu version grossed a further ₹1.40 crs. Likewise on the opening weekend in Australia, it grossed ₹50.82 lakhs and in the UK, the film has grossed ₹46.62 lakhs. Trade pundits remarked that the film was a "trade favourite" in the overseas market and predicted massive profits for the producers.[9][71] Ten extra screen were added for the second week of the film in the US, and within a week, it became the second highest-grossing Tamil film of 2015, behind I.[72][73] The film subsequently completed its run in the US, finishing at number seven on the all-time list. Similarly in the UK, the film completed a month-long run at the box office, unheralded for a film not featuring an established leading actor.[74]