Wrath's Awakening

What happens when a medieval world of swords and steel is invaded and forcefully introduced to a System of levels and magic?

It was just another ball.
Princess Cassandra thought she could deal with it.
She just had to pretend for half an hour to actually care about the attending nobles before her father would let her leave, as usual.

That is, until the sky started glowing blue and strange text appeared in front of her face, mentioning something about a System.

Even that she could deal with.

But being kidnapped by planar invaders from some planet called Earth after a glowing heart flies through a portal in front of her and disappears into her chest?

That might be a little too much.