Kill Me Baby/WMG

Yasuna is the adopted child of Kirika and Mireille.
They did not train her how to kill people; but they told her at a young age what they used to do for a living. This is why encountering a child assassin doesn't surprise Yasuna at all. (That's what Mommies used to do!) Sonya's organization is not officially a rival to Soldats; but strong enough of an independant faction to make their school enough of a Truce Zone so that it was decided to be the safest place for Yasuna to go to school. One of her parents tend to watch from a distance to make sure nothing really serious happens.
 * They are not interfering with Sonya because it's pretty clear Sonya has no problems with what she does. Sonya also once killed a Soldats agent sent to the school to kill Yasuna; which is another reason she's tolerated as Yasuna's friend. (Sonya's organization and Soldats had very strongly worded diplomatic reactions to this to solidify the school's Truce Zone status.)
 * Agiri has been hired to see if there's ANYTHING "True Noir" inherited or learned by Yasuna. Short answer: ...no. Long answer: Hahahahahahahahaha. She keeps testing because her superiors don't believe it and because it amuses her.

Sonya is Russian
She is clearly a victim of Phenotype Stereotype, her name is, while not common, used in Russia and, finally, there is openning music.