Nikhil and Swati had previously working in last year's Telugu blockbuster "Swamy Ra Raa.
"Swati was signed because our last film was a hit and this was a decision taken by my producer. I enjoy working with Swati because she knows the language (Telugu and Tamil). When you're working with someone who knows the language, you're performance as an actor automatically improves," Nikhil told IANS.
"I always believe that when you work with an actress who knows the language, you're performance improves by about 30 to 40 percent. Moreover, audiences like her too and she's a crowd puller," he added.
Directed by Chandoo Mondeti, "Karthikeya" also features Rao Ramesh, Tanikella Bharani, Nassar and Tulasi.