Ever since Rainbow Brite was born, Rainbow Dash and Flash haven't been able to have dates like they used to before the filly was born. So they left the babysitting to Twilight.
Twilight loves caring for the little girl, and she forgets all her troubles. Until Blueblood shows up.
She has one more day to enjoy life in Ponyville.
One more day to have Spike as her number one assistant.
One more day.