Showdown on the High Seas is the twelfth episode of Granblue Fantasy: The Animation. It is the final regular season episode of Season 1.
Mizarea, the capital of the Auguste Isles. Leviathan continues to wreak havoc there while Eugen and the other soldiers fight back. Gran returns with the awakened Lyria and the others to Auguste, but are stunned to see the city in its current condition.
Eugen meets up with Gran and company, and relates that they’ve decided to evacuate from the island. Gran and the others stop him, though, as Lyria senses that Leviathan was doing everything it could to purify the polluted sea. She also relates that Leviathan’s life is tied to the others and that it draws on their life force.
Lyria is determined to help Leviathan and Eugen vows to aid her. At the same time, Mary, Karva, and other skilled knights begin working to protect Auguste.