I hope you all agree this falls under the jurisdiction of usage and not opinion : )
So what nicknames are currently in usage for the name "Kira" (or Kiera, Keira, etc). I do fully understand that the spelling Kira is either a Greek title, similar to Madam, or the feminine Russian form of Cyrus via Kiril. As a Russian name i have found the diminutive Kiroshka. Its a great nickname but i don't know that you could convinve Americans to warm up to it.
Spelled that way it is also Persian for "sun". I can't find any nickname trends in Persian, so i'm hoping someone who reads this will have had experience with how that works.
Same with the celtic homophone, Kiera/Keira/Ciara. I'm just not familiar enough with how that nicknaming system works either.
I look forward to hearing all the different derivatives you've all come across! Thanks!