Despite common opinion, Bruce knew his own limitations.
He knew that he had a breaking point, a weakness.
A weakness that no one (fortunately) knew about.
And that breaking point, that damn weakness, had a name.
Richard "Dick" John Grayson-Wayne.
Bruce had long ago come to terms with a grim but true thought: the only thing that would trigger Batman enough to cross his no-kill line was Dick's death itself.
When Jason had died Bruce's first thought was to kill that bastard Joker but in the end Superman kept him from crossing that line and for that, although he would never admit it to the Boy Scout, he was very grateful.
But Bruce was sure that he would not hesitate for a millisecond to kill Dick's killer, even if he had to travel to the edge of the universe.
Not even an entire army of Kryptonians could have stopped him from killing his eldest son's killer.
However, Bruce could not say the same for the rest of his sons because either Superman (or someone else like Alfred or Dick himself) would stop him from killing, or because Nightwing himself would kill his sibling's killer.
As happened to the Joker.
Bruce could not imagine living his life without his firstborn.
Sure, all his children help keep him grounded without making him commit idiocies he might regret in the future.
But Dick was in a different category altogether. He was Bruce's heart, soul and spirit.
And without Dick, Bruce could not live.
These are the headcanons that have been running through my head. I will mark this work as complete but if I can think of other chapters, I will add them without problems.
Thanks folks for your support, and (probably) see you tomorrow with the start of a new story!