Most people don't realize the huge dichotomy that is both life and death.
She does. Despite being young and incomplete and deceptively uncomplicated, she knows that Mugen is a dead man walking -- it's there in the complex weave of his movements, the monkey-like agility and the reckless edge of calculated insanity that he rides with impunity. She knows, too, that Jin is alive where Mugen isn't but also dead where Mugen isn't, encased in the frost of his control like a firefly in amber.
Still, ultimately it's not Mugen's fault that he's such a pretty corpse. It's not Jin's fault that his coldness has rendered him fragile and brittle and so, so close to shattering.
It's not Fuu's fault that she can't decide.
And so at night she allows herself to be trapped between them both, hungry for the feel of their hands on her baby-soft skin smoothing over the angles of her hipbones and lower still. Mugen is silent, an impression of heat and sweat-slick skin against her slender back; Jin is cool and broken, brushing wet hair away from her heated cheeks, her name spilling like pearls from his lips, "Fuu, Fuu."
Every night without fail, crushed between them, she kills the dead and the living alike, watching them unravel violently as she burns them with unwanted kindness.