That Time I Got Reincarnated as a Slime the Movie: Tears of the Azure Sea

The second movie in the Tensei Shitara Slime Datta Ken series.

Fresh off celebrating Tempest’s founding festival, Rimuru and his companions are summoned to the Sorcerous Dynasty of Thalion, a nation of elves, by its influential empress, Elmesia. But their well-earned rest at her private resort island is cut short when a mysterious girl named Yura shows up, kicking off a new adventure on the endless azure sea..

(Source: Crunchyroll)