First, let's get the big one out of the way: Arthur and Mera had a baby boy! A man of two worlds who claimed to hate Atlanteans and an Atlantean who initially viewed humans as filthy savages came together and perpetuated the races of their supposed enemies.
The Tickets on Sale trailer opens up with Arthur bonding with his son when he sees the little tyke staring at their fish tank.
Before Arthur and Orm head to Necrus to save Arthur Jr, Atlanna embraces her two sons. The oldest, a son of the land, the youngest, a son of the sea, but both brothers are equally dear to her.
"The two of you, standing together as brothers... Promise me you will protect each other.."
Arthur, Tom, Mera and Atlanna all spend time together at Tom's lighthouse. Not only does Tom get to have a full family for the first time in decades, but it shows that these three Atlanteans of royal upbringing still make the time to enjoy the simpler parts of the surface world.
While Orm isn't exactly happy to see his brother again or to discover that their empire is facing problems under his amateur rule, he no longer berates Arthur as an inferior mongrel, going as far as encouraging his older brother to be the best king he can be.
"You're not as bad at this as you think."
"If you lead, the Seven Kingdoms will follow."
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The sheer excitement Arthur shows over having a son. Once he finds out that Junior inherited his ability to talk to sea creatures, Arthur seems positively ecstatic that he's not the only one now.
None of the Royals - Nereus, the Brine King, even Orm - refuse aid to Arthur and Mera in saving their baby boy and all join up on a rescue mission to get him back.
In the aftermath of Manta's kidnapping of Arthur Jr., Atlanna stays by Tom's side.
Nereus isn't ready to forgive Orm, arming him with a small axe while the rest of his troops get high-tech weaponry. Just when Nereus is on the ropes and it seems like Orm will seize the opportunity to go back to his villainous ways, he instead chose to rescue Nereus. The king rewards the gesture by handing Orm a blaster.
When Kordax tries to pit Arthur and Orm against each other, hoping that the losing party will release him, memories of the ring of fire from the first film play through their memories. After all they've been through, the two brothers held onto the moment where they both admitted how saddened they were at the thought of being enemies.
In the climax when everyone is trying to escape a collapsing Necrus, Black Manta falls down a crevasse, and Arthur reaches out his hand to save him. David rejects the gesture and lets himself fall to his apparent death, but Arthur was willing to spare the man who kidnapped and tried to sacrifice Arthur Jr. In the previous film he'd expressed guilt that his callousness (letting his father die) drove Black Manta to vengeance and despite the latter's crimes against his family, Arthur thought about the choice he made in their very first encounter and went for a better course of action.
Shin proves he has a conscience by protecting Arthur's baby from Manta. Though he fails, he is rescued by Nereus and Mera gives him a kiss of thanks.
At the film's end with Atlantis revealing its existence to the surface world, a pleased Stephen Shin is seen watching. Having been deemed a crank and liar over his claims of Atlantis, he has finally received vindication.
