Well, Batman, when a German man and an Asian woman love each other very much...
Naw, not going down that road. Though I'm all for international relationships. They're so cute! <3 I'm assuming she had it in her lineage somewhere, but that still wouldn't explain a lot of things.
Maybe her father walked out after a while? Left the children weapons of European make, and just. Got up and left, like the general he must have been, to fight in a war, and just died there, leaving the mother's family to raise the children by themselves and so of asian culture and stuff?
I don't know. Throwing around suggestions here as to why.