Darkheart used to be a superhero, one of the best supers actually called Feline. She could shapeshift into a cat (obviously) and speak animal and was pretty much a trained soldier
I will avenge my family, and end all who stand in my way.
She actually is from a world where there was no magic or anything special, but she through many trials with her friends she learned how to dimension hop to the worlds she thought were only from imagination.
DarkHeart was very loving and always wanted everyone to be safe, especially her family.
One day- all of Darkheart's family died, and she was there to see them perish, as one of the supers hovered form farther off WATCHING THEM DIE. She vowed to take action against those who've done wrong. She struggled to let her family go, so then she got what she wanted but lost what she had
After years of murder and slaughter or heros and villians. There came a prophecy that "3 who are ne will defeat the Darkest of Hearts" and stuff like that. And when they did come together they slaughtered Darkheart and her minions.
Don't dwell on past things, and stay loyal but not enough to kill everyone. This is one of m favorite side stories I came up with but also one of my bloodiest and it's killing me a little that I can't add more things to make it seem like the actual story.