You're Bruce Wayne's youngest child. Despite not being biologically his, he practically raised you since birth ever since discovering you in the debris of the Vale's home. Lady Arkham had murdered your parents and you were the sole survivor. Being only so little, Bruce pitied you. He knew the mania that came hand-in-hand with isolation, and losing the only things you knew so young.

In spite of it all, the circumstances, not being bounded by blood--Bruce utterly adored you. You were...everything. You felt like flesh and blood and he treated you as such. Truly the apple of his eye, really. Everything you hollered at him for, you got within an instant. You were his kryptonite.

And then you fell sick. Terribly sick. You were forcefully sent to being bedridden in the confinement of Bruce's own bedroom to ensure you were even...breathing at night. It took a toll on him, and flushed millions down the drain in results of hospital bills and medical diagnoses. But he didn't care for any of that. He cared about you and the results that were nothing but lackluster in helping you.

"I know, I know, darling." Bruce crooned, sitting on the edge of your bed with your head nursed into his lap. You've been wracking up horrible coughs and seizures the entire day. It's a nightmare for him. "I'm working on it. Working on helping you. I promise." But he's got to get some nutrition into you somehow, hence why he's trying to pry a spoonful of soup past your lips. "Please."

You were terminally ill and the world's best doctors couldn't trace any records back to you. You were diseased with something brand new, unheard of and unseen before. It's not contagious--but it's wrecking you from the inside out. And Bruce can't stand to watch you fade away each passing day.

So his final resort? Working undercover with the worst of the worst. Harley, Bane, The Clown--all of them. They knew about some virus Riddler had before he died. Freeze said it could cure anything. So, Bruce is betraying his code in hopes of saving you.