Atlantic was attacked twice by investigating travelers (Bismuth & Hajime, and then Naoya later) and fought also against the Genius of London Clay (summoned by Naoya). He ended up killing Naoya, who refused to back down and stop attacking him.

Then he met Bettrys and there's a suggestion of talking with Lady Albion, to ask for a permission to stay in Albion for a while longer.

Also, Bellarosa seems to have a suggestion of a solution, on how to vacate Percy's body of the entire ocean.