A Christmas to Remember

You come from a very disfunctional family, but you have know Vash and his sister for eleven years, being with them more than your own family. Eventually it came to the point where Vash and Lili's parents took you in to live with them full time.
But, a few years back, their parents died, so you and Vash became a father and mother of sorts to Lili's. It's nothing romantic... yet...
But this year Lili turned 15, so you decide to give her a special Christmas to Remember.