The following story contains all sorts of spoilers for Aquaman, so bail out now if you haven't yet seen James Wan's blockbuster film!
The end-credit sequence is no guarantee in a DCEU movie. Some of the films have them, and some of them don't. Some of them tease movies that we might get, while others (cough, cough, Justice League) tease supervillain pairings that may never pay off.
James Wan made sure to put a fresh beat into the middle of his Aquaman credits, and it builds on two characters who had their stories gradually develop over the course of the film. It establishes a direction for Aquaman 2... even though Aquaman 2 hasn't yet been announced. (It will happen, if the box office receipts keep flowing in the way that they already have!) What happens in the end-credits scene of Aquaman, and what could it mean for a future film? Let's discuss, in depth. Get it?
Shin Meets Manta
The Aquaman mid-credits scene opens in a nondescript room, where a character we have seen in the background finally gets something important to do. Dr. Stephen Shin (played by Fresh Off the Boat star Randall Park) is tinkering with the technology found in Black Manta's helmet.
That's right, the villain, played by Yahya Abdul-Mateen II, survived his fight in Italy with Arthur Curry. The last we saw of Black Manta, he was bouncing off of the cliff rocks and plunging into the ocean. He's beaten and bruised, and his costume is badly damaged. But he's intact, and laying in a bed, wrapped in bandages.
Over the course of the movie, we have seen Stephen Shin on news telecasts warning us that the oceans on our planet are filled with Atlanteans. He seems to be convinced that whole races of alien beings exist in the seas, and he uses the fact that Aquaman (Jason Momoa) now walks among us as a warning sign that the surface dwellers -- humans -- might quickly lose our spot at the top of the food chain.
Dr. Shin's warnings grow louder and more severe when Orm (Patrick Wilson) sends a warning shot over our metaphorical bow, pummeling our coastlines with a tidal wave that leaves ships, and a lot of trash, on our shores. This sets Shin off on a tirade, though many dismiss him as a crackpot conspiracy theorist.
The walls in Shin's room suggest that he is a bit of a conspiracy nut. They're littered with newspaper clippings, maps and photographs suggesting a lifetime of chasing dead ends about Aquaman. Though Shin's about to have all of his fears confirmed.
Once Black Manta wakes up, Shin asks him if the helmet is Atlantean tech. (We know that it is.) Manta warns him not to tinker with the dangerous outfit, and Shin soon learns why. He triggers something in the helmet, and the eyes fire that deadly red Manta beam, taking out equipment on Shin's shelves and his ceiling.
Shin demands to learn more about the Atlanteans, and Black Manta agrees, but first, he says, he wants to know everything he can about this man. He flings his trademark knife across the room, and it buries itself into a photograph of Arthur Curry, landing right between his eyes.
How This Connects To The Comics
James Wan's Aquaman has several distinct ties to Geoff Johns' popular run of Aquaman stories in The New 52 version of the classic hero. And it's in there that we see how Aquaman 2 might develop the partnership between Black Manta and Dr. Stephen Shin.
In the books. Dr. Shin is an expert on all things Atlantis, and over time, he is used by Aquaman and Mera as a resource to research things they might need to complete a quest. However, in one major change from the movies, Shin is a friend of both young Arthur Curry and his father, Tom. He's seen as an ally (initially), though the more he pushes Arthur to learn about Atlantis, the more the hero keeps him at bay.
The movie doesn't establish that relationship. Randall Park doesn't share any scenes with Jason Momoa, though Aquaman 2 could show some scenes of young Arthur and young Stephen, showing a link that we just never got on screen here.
In the DC Comics, the more that Aquaman kept Dr. Shin from learning about the mysterious Atlantis, the more that the scientist sought assistance... often finding it in Black Manta.
So yes, these two characters often did collaborate in the comics, though Stephen Shin frequently played a complicated role in the struggle between Aquaman and Black Manta. The villain often used Shin as a pawn to manipulate Aquaman, and there are times that Shin -- though mostly loyal to Tom and Arthur Curry -- betrayed the King of Atlantis to satisfy his own need for more knowledge about the underwater kingdom. Stephen Shin is not a clear-cut ally for Aquaman and Mera. Though, if and when Aquaman 2 takes place, it seems like Shin will very clearly be working against Aquaman, and assisting Black Manta.
What This Means For Aquaman 2
This means that Aquaman 2 already will have two villains, and they are characters who we have met before. It makes sense to bring Black Manta back. He and Aquaman are such mirror images of each other, as they both are furious at someone else for "murdering" their parent. (Though, in Arthur's case, Queen Atlanna actually lives, so....)
And in the case of Dr. Stephen Shin, we only see him in a few brief scenes, but his obsession over Atlantis gives Aquaman 2 plenty to explore, especially when you pair him with a powerful being who has encountered Atlantean people already, and has had access to their weaponry.
Speaking of, Orm, who manipulated Black Manta, is only jailed and not killed, so the chance of him coming back can be high.
Aquaman 2 likely will have to introduce some new characters, however, so it doesn't just tread the same waters that are explored in this new movie. While we are a LONG way away from casting any sort of sequel -- heck, the sequel hasn't even been announced yet -- characters who make sense in a story involving Black Manta and Dr. Stephen Shin would be Ya'Wara, the Goddess of the Amazon jungle, and the members of The Others. That would include Klone, Racket, Guardd and Rebound. So we shall see if this comes to pass!