Lightgiver
Not a fan of this, at all. Marvel already has dangerous villains that could kill the firekeeper. But you decided to add the good hunter from bloodborne? The dude who kills Eldritch gods of blood, madness, and insanity? The dude who can become a god himself at the end by consuming the three umbilical cords? And then you basically make him useless by making his old blood be connected to the first flame and the dark sign? Something the firekeeper is able to take away as she pleases? Kinda makes it worthless to include him in the first place unless you can make him independent of the first flame and the dark sign. And even then it would make it tricky to write the encounters considering if the firekeeper dies then that's it, story ends, nothing else to say. So you would have to make up situations that would ultimately have the firekeeper either win or survive without making it seem forced. Which then downplays the villain and what he can do as the good hunter at the end of his bloodborne journey.