Okeanos (Fate/Grand Order) Wiki

Third Singularity: Sealed Ends of the Four Seas, Okeanos

The third singularity in Fate/Grand Order. It's set in the year 1573 in an endless ocean, after Francis Drake went on a voyage and encountered Poseidon in Atlantis, where she defeated him and acquired his holy grail. Due to another holy grail being inserted in the era as part of the plot to incinerate humanity, the energy of the two competed together resulting in the endless ocean.