Amber Heard's Mera will be introduced in next year's Justice League, but we shouldn't expect it to be a very significant role. We'll have to wait until the Aquaman standalone movie to see her in a full-fledged role. James Wan is set to helm the movie, and in a recent interview with Bustle, he talks about the relationship between Mera and Jason Momoa's character, Aquaman.
Comparing the Aquaman movie with Raiders of the Lost Ark and Romancing the Stone, the director reveals that he wants the movie to feature "the classic action-adventure-romance aspect", which he thinks is "kind of fun". From what he adds, it seems like he is playing up a hate-turned-love relationship between the King and Queen of Atlantis:
It starts off initially with them not quite clicking with each other. But then, as the story progresses, as they learn to try and work together, they get closer and closer. I think those stories are always such a great place for a filmmaker like myself to have fun with my actors.
Wan claims that the dynamic between Aquaman and Mera in the July 27, 2018 release is going to be "really interesting", as Heard's character is "super strong" and "very powerful". She is someone that you "don't wanna mess with". He explains:
I think Amber will bring that sense of strength, but at the same time, we also want someone who has a sort of feminine quality to her, as well. She's a bit of a contrast to Momoa, who's more of a muscular machine, almost.
With a script penned by Will Beall that's based on a story treatment by Wan and Geoff Johns, the Aquaman movie will start filming early next year in Australia. So we can expect to come across more details on the project in the coming months.