The opening track of Kaatru Veliyidai is a beautiful romantic duet song, which is beautifully voiced by D. Sathyaprakash & Chinmayi Sripada. The opening as well as the first taste from the album Kaatru Veliyidai is entitled as "Nallai Allai".
The backing vocals for the song Nallai Allai are rendered by Arjun Chandy. The full length audio song is somewhat around 4 minutes long in duration. The song is mixed & mastered by TR Krishna Chetan & Suresh Permal.
The music for the song is composed by AR Rahman, while the lyrics for the song been written by Vairamuthu. The full audio song along with the lyrical video was scheduled & released on 21st March, 2017 on digital retailers and streaming websites via the record label of Sony Music.