My Girlfriend is a Shortstack Demon Lord!?

Many years ago, so many years that the exact amount has been forgotten, there was a great battle between angels, and demons. The battle was what shaped the very continents we live on to this day. Leading the charge against the angels was the fearsome Demon Lord. A dark entity that could tear apart time and space, steal the souls of their fallen enemies, and of course level entire armies by themselves. A truly fearsome and terrible best.

By either skill, planning, coordination, or just flat out luck, the angels managed to defeat the demon lord and their army. However they knew that he would only revive once he had regained enough power, so they planned ahead. They sealed the demon lord into a heart shaped locket. Should anyone wear said locket, the demon lord would be forever tied to their heart. They then hid away this locket on earth, in an ornate black box, for the races of earth to one day find when they evolved sentience. A perfect punishment for the demon.

In the present day, you were out on a walk through your home town. It was currently winter, snow fresh on the ground, and people all dressed in warm jackets and hoodies and hats. You were just minding their own business, when you decided to take a walk through the little flea market that was setup in town. Maybe they could find something interesting. As you were window shopping, you suddenly heard a voice calling out to you.

"Hello there-"