Twenty-year-old Kizie Basu is fighting thyroid cancer when she meets Immanuel 'Manny' Rajkumar Junior, who has previously suffered from osteosarcoma and is in remission. Manny and his friend Jagdish "JP" Pandey, who is suffering from glaucoma and is blind in one eye, are making a movie together, inspired by well-known Tamil actor Rajinikanth. Manny invites Kizie to be the female lead. The two bond over his love for Rajnikanth's movies and her love for music, specifically an incomplete song by retired songwriter Abhimanyu "AV" Veer Singh. Kizie and Manny gradually fall in love as they shoot scenes for JP's film named 'Rajni Aawat Hai, Sapne Jalawat Hai'. They decides to make 'Seri', the Tamil word for 'okay', their secret word that will help them remember that everything will be okay in life and to stay positive. After an operation, JP loses sight in his second eye, making him go blind.
One day, Manny informs Kizie that he has managed to track down Abhimanyu Veer and get in touch with him. Kizie e-mails Abhimanyu Veer, who replies that she can visit him in Paris, where he lives, to get her questions answered. Kizie and Manny convince Kizie's parents to allow them to take the trip, with the condition that Kizie's mother joins them. As they are making arrangements for the trip, Kizie's cancer gets worse and she is hospitalised.
After her recovery, she is weakened and initially distances herself from Manny but later relents. They go to Paris to visit Abhimanyu Veer, who turns out to have no conclusive answers, disappointing Kizie. Soon after, Manny informs Kizie that his cancer has returned and is now terminal.
As Manny's health deteriorates, Kizie convinces him and JP to finish the film. Manny then invites JP and Kizie to his mock funeral, where they deliver eulogies that they have both prepared. Manny dies a couple of days later, leaving a letter for Kizie, explaining that he had finished Abhimanyu Veer's song for her and had even convinced Veer to help him finish the song.
JP's finished film premieres in an open-air theatre, where Kizie and the crowd, consisting of their friends and family, get emotional. In the final scene of his film, Manny breaks the fourth wall and directly speaks to Kizie, telling her to live life to the fullest, to which she replies "Seri".