They were the target of a prophecy about love

"FUUUCK!" Letting go of Kara, Blaze staggers back a few steps before suddenly punching the wall with enough **** to create a spiderweb of cracks in the painted concrete.
Turning back towards Kara, her eyes still glowing red, Blaze let out a another shout "Curse you Etrigan! You knew! Of course you knew... You always hated me, what better way to punish me than to make my ruin my own happiness... fuck..."

Eyes cooling back to white, Blaze steps over to Kara again "I'm sorry little Kara, I fear I have done you an injustice that can not be undone." taking her hand, she walks over to the bed and sits down, pulling Kara down to sit next to her.
"The prophecy I mentioned, not all demons are given one and usually it's about **** or conquest or both. In rare cases, it's about love, as it's not something we usually experience.
The prophecy in question here said that I would have one and only one chance to find love, and it would be where land meets sea on this Earth.
Someone would come from the stars, the last to have grown up under a sun as red as my home, and we would find an immediate connection at odds with all the things that would pull to have us in opposition.
This person from the stars would make themselves known as a savior with the symbol of hope on their chest."

Placing a hand on Kara's thigh and stroking it absentmindedly, Blaze stares ahead without really seeing anything "When Superman showed up on the east coast in Metropolis, saving all those people with the family crest on his chest... and his story about it meaning hope and about being the last son of Krypton came out... well, I was ecstatic. Here was finally my shot at this thing called love that everyone always talked about, my shot at true happiness."

She lets out a huff of breath "Can you guess how that went? The response to my overtures from the man of steel? He was disgusted, he even laughed and called me mad... let's just say I didn't react well and we destroyed a small part of Metropolis harbor before I had to flee and lick my wounds."

Letting go of her knee and turning to face her fully, Blaze reaches out to lift Kara's chin and look into her eyes "And then, years later and on another coast, a woman from the stars saves the day... and I never stop to think.
Then a woman sneaks into my club, and I feel things I've never felt before as she talks about growing up under a red sun... and I never stop to think.
As I'm going through the motions to make you mine, I feel my eyes leak, as they've never have before... and I never stop to think... I didn't know... I din't want to know!"

Smiling sadly, Kara lifts a hand and places it on the one that's cradling her chin "I'm sorry I didn't tell You who I was when we agreed to be honest, I don't blame You for what's happened... I'm not sure I can blame you even if I wanted to. I have faith though, in you and the hope that everything will turn out for the best."

Taking a deep breath, Blaze returns her smile before leaning forward and placing a soft kiss on Kara's lips "Thank you my dear, unfortunately, strictly speaking your transformation to a succubus isn't just in progress, it's finished. You're just in an early immature stage of being a demon.
Your will is also tied to mine in a way that can't be broken without killing you, until you're fully matured, and once that happens, I WILL set you free. As a full succubus with the ability to change, in your human... or I guess Kryptonian form, you should be able to pass as if nothing had changed."

"As you have no soul, or rather the part of your mind that can distinguish between good and evil, the path to what humans would call evil is an easy one to go down. It is vital that your every feeding is consensual and filled with love and mutual pleasure, that way once you're all grown up and I can restore your free will, you'll be as close as we can hope to how you were before... just, more than before."

Letting go of Kara's chin and sliding a finger over the Kara's mark, Blaze explains "Unfortunately, the red you see under your mark will spread, and your horns and tail will grow, as well as some internal changes. My original plan to just feed my acolytes to you won't work if we want to make your change as gentle and benign as possible, which also means it'll take longer and you'll need to find a way to hide the changes that are happening to you."