In the Sci-Fi world, it's best known as the name of Kira Nerys, the Bajoran first officer on Deep Space 9. Bajoran naming tradition used the surname first, and given name second, so Kira was her surname, and Nerys was her given name.
In Fantasy, Kira was the name of a gelfling in the film, The Dark Crystal.
For Gamers, Kira is a character in the video game Mortal Kombat.
In 2011, Kira ranked #333 in the U.S. This makes her a familiar, yet uncommon choice.