The Villainess' Wise Retirement Plan

I've transmigrated into a game I used to enjoy playing, "The Demon King's Consort," as the villainess who dies after harassing the female lead!
Worse still— I have a terminal condition! As a human mana stone, the more I use magic, the more it drains my life force...

What kind of life is this...?

No matter. I can simply just choose not to use magic, right?
I'll preserve and protect my mana (= life force), gather a slush fund, and run away with my big sister to a warm and peaceful southern country...!

Or so I thought...

"Take it, Lillian. It's your doll."
My Father threw the male lead at my feet. The obsessive male lead that was destined to become a psychotic, possessive king in the future...!