Wonderful story! I like how it touches, not only the their established relationship (I have a weakenss for happy, well-established relationships of any kind), but also on how their past made them who they were. I really like how you resolved Illya's problem from having not going through the same procedure as Napoleon when he left the Command.
The only part I didn't like was how much they've aged by now... *sniff* meaning either a wind-down of stories in this delightful series or... worse!