Damian Wayne revealed!

Inner Demon

It had been a secret among Damian's maternal gamily, the Al Ghul's. Not even the assassins knew. Thalia had kept it a secret.. No, not the part where she told Bruce their son had died in order to keep Damian. He had actually died as a babe... But the part where he had come back to life, and it wasn't by using the Lazarus Pit, was a secret only known be her as she killed the nurse maids.
He'd suddenly came back to life, 10min after he was dead, with no explanation. He had cat-like eyes and horns for a while before they receded an hour later.

She didn't know how or why he had died right after his birth or came back to life without the Lazarus pit.

And she still didn't know when Damian had turned 10 years old and she took him to her beloved, his father, for safe keeping as the League was threatened.
She also hadn't told Bruce about it, in hopes that he didn't investigate Damian's life with her at the LOA.
He already had enough trouble finding out information about them. And she was sure Damian would never betray his family.

Unbeknownst to her, Damian himself kept a different secret: He was aware of everything since his birth. Including the fact what his grandfather wanted to use him, more precisely his body, for.

Of course, as he was a babe, he didn't understand what they were saying yet, but at night or when he was surrounded by darkness, everything was crystal clear to him and a soft but deep whisper talked to him, like a bonfire cracking near his ears, telling him cruel secrets as if it were a lullaby for only him. Much later, when he was trained and sent on his year of blood he also hadn't been alone, not counting the Assassins coming after him. The voice had followed him, giving him strength and advice, while filled with glee.
It sounded like his voice but a few octaves deeper. He had referred to it as 'a calling of the night' or simply 'Demon' as it was always near him. Which, as he found out, might be because others didn't hear him so he kept it secret that he did.

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So when he finally met his father, the notorious Batman, while being a nervous wreck on the inside and Demon seemed to be even stronger than normal in Gotham, he was on edge. But on the outside he was moving as fluent as possible with an attitude befitting of an Al Ghul - successfully annoying his father even more than his sudden appearance already did.

He had trouble understanding his father's 'justice not vengeance' moral code and 'no killing' rule. For the former, no one had wronged him so he wasn't being vengeful. Maybe Drake as he believed the other stole his position so a fight for succession had seemed in order.
As for the latter, only by killing would the world be saved.
That's what he had been taught, that's what he agreed with and what Demon also agreed with - against the logic of Batman.
Surely his father was smart enough to know too; if one kills more than one killer their numbers would decrease and, following that, so would crime.
Even the world's leaders and prominent figures would resort to crime in order to benefit from it. Some of which even employed the LOA to get the job done.

Killing a person for a specific crime was still allowed under the law in some countries too.

It was common knowledge.

But his father's method wasn't a long-term solution and crime would continue, like the Joker who did kill without remorse while his father watched without ending it, only preventing it to what he believed was possible. Even with the victims' close people rather wanting to get a hit on the defenseless Joker with a gun, it wouldn't be his 'justice'.

Like when the man had killed the second Robin, Jason Peter Todd, but Batman still hadn't killed him even after that. And when Jason was revived by his mother and revealed himself to his father he had openly said that he was furious and disappointed he hadn't killed the Joker - 'screw his moral code' were his words.