Chekhov's Gun: The herbs that Kira is taking for her pregnancy. They render sedatives ineffective, which allows Kira to surprise and kill Silaran.
Children Are Innocent: Kira manages to save her bacon by exploiting Silaran's belief in protecting the innocent, i.e. the baby.
Gray and Gray Morality: The killer claims, persuasively, that Kira killed innocent people whereas he never did, such as a bomb she set taking out not only a brutal Cardassian war criminal, but his entire family too, along with anyone in the immediate vicinity, whereas he goes out of his way only to target them, and even spare the life of the unborn child she's carrying. Kira retorts that every Cardassian on Bajor, even if they just folded shirts as a servant shouldn't have been there and were guilty legitimate targets. True, she's talking with a calculating, cold-blooded killer, but it drives home that, yes, Kira was a terrorist, and from his point of view he is the "light" to her "darkness". Kira's only real reply is the old idea that the one cannot exist without the other, or as she says "the light is brightest in the dark."
I Did What I Had to Do: Viciously deconstructed. Kira tries to use this justification and Prin immediately calls her out on it. She didn't have to use indiscriminate killing to fight the occupation, she just didn't care enough to find another way.
Imperiled in Pregnancy: A very pregnant Kira is lured to the Serial Killer's hideout, he stuns her, and then attempts to cut Kirayoshi out of her (the intent was to save the innocent baby and take revenge on Kira). She manages to turn the tables and shoot him.
Pregnant Badass: Just cause she's knocked up doesn't mean Kira can't still kick some ass. Just ask those poor security members who get in her way.
Tele-Frag: Prin plants a "remat detonator" on one of his targets. When Dax and Worf try to beam her up, the device kills her by scrambling her transporter pattern.