- "What's in the three boxes?"
"It's ancient history."
"What is it? Mankind's melting the polar ice caps, destroying the ecosystem. They got it coming?"
"Hey, I don't mind if the oceans rise."
"How about if they boil?"
"Dressed like a bat. You're out of your mind, Bruce Wayne."
"Doesn't mean I'm wrong."
- ―Batman and Aquaman[src]
After he declined Batman's offer and left Iceland to departed back to the ocean, Arthur rescued a sailor caught in a storm, taking him to a bar where he deposited him on a table and ordered himself a drink. The sailor then described having been attacked by a strange creature, as Arthur looked at his own hand and noticed a green strange substance in it. Realizing that there was something wrong happening, Arthur finally decides to enter in Atlantean territory.
- "You dare speak of Queen Atlanna that way?"
"Your 'queen' left me on my father's doorstep and never gave me another thought."
"Your mother left you to save your life! You cannot imagine how it hurt her, what it cost her. But you're not a defenseless child now. It would have been her responsibility to follow that monster to the surface and stop it. Now, it's yours."
"Then I'm gonna need something from you."
- ―Mera and Aquaman[src]
After the Attack on Themyscira, Steppenwolf attacked an Atlantean Vault of the legendary and ancient city of Atlantis to retrieve the second Mother Box. The result ended up being nearly the same than in his previous attack. He ultimately managed to retrieve the penultimate Mother Box from the Atlanteans despite their efforts and the help their leader Aquaman, who was saved by Princess Mera, prompting Aquaman to accept Bruce Wayne's offer to join the newly formed Justice League.
Mera then spoke with Arthur, who had grown estranged from the Atlantean half of his dual heritage, revealing to him that he hadn't been abandoned by his mother like he'd believed and that her love for him should be what inspires him to protect his people. Pressing further, Mera stated that retrieving the Mother Box is what his mother would have done.