Ozai sat across from him in the cell and laughed and laughed, like he'd never been more entertained in his whole life, as he was by Iroh in this moment. He finds Iroh hilarious. He finds Zuko hilarious. He finds the idea that Iroh is "like a real father" to Zuko to be the most amusing of all. He sarcastically wished Iroh well in this endeavour. "Good luck with the world's most disobedient, stubborn and stupid child."
Something cruel shifts in Ozai's face then. Even through the laughter, you can see the deep unkindness of spirit etched into the lines on his face. He turned his head, like a komodo rhino smelling a meal, and said with a slow drawl "You know Zuko has a very similar brand of stupidity to dear Lu Ten. Explains why you gravitated to him so much after poor Lu Ten met such an untimely death."
Just the name Lu Ten is sacred to Iroh. It normally conjures up that warm summer afternoon feeling. Warm breeze, cool tea and laughter.
Ozai saying Lu Ten's name feels like a gross intrusion. A violation. The gleeful way he says "untimely death" makes something large, dangerous and long buried in Iroh, shift a little and rear its head. Iroh used to refer to this feeling as unleashing his inner dragon. Ozai does not realise the danger he's in, as he continues langiudly, with a false warning. "Stupidity really will get Zuko killed one of these days...and I'm betting on sooner rather than later."
The veiled threat sets the Dragon loose. Iroh is not aware of much aside from the flood of anger and his own body. Iroh is strong. The muscles in his arms are like the cables that hold up the gates of Azulon. Ozai was taller and bigger at one point, but he has wasted away during his time in prison. Ozai's expression is frozen in horrified surprise as he sees Iroh bearing down on him.
Ozai miscalculated. He thought the mention of Lu Ten would draw Iroh back into that crushing depression that ensued after Lu Ten's death blew a hole in Iroh's world. Just the whisper of him used to send Iroh back into that gaping void. But not any more. Iroh finally feels like he has become the man his son would have been truly proud of – and that pride gives him strength.
The dragon inside roars with rage, in sheer indignation that this man would dare to threaten Zuko in his presence. The depths of Iroh's protective fatherly instincts are uncharted. Like on the firenation maps of the far eastern sea, Iroh was sure that there was monsters there. If he could have, he would have warned his brother abandon all hope, yea who trespass here.
-o-
this one is for boogie-boy, who asked for this little insight ;)
On old-school (16th century old school) British nautical maps they used to write on the un-chartered sections "abandon all hope yea who trespass. Here there be monsters". It just tickles my funny bone to see that written all over where Australia is. Oi england, why don't you tell us what you really think.