Tensei shitara Slime Datta Ken Movie 2: Soukai no Namida-hen

After Tempest's opening festival finally ends, Rimuru and his companions accept an invitation from Emperor Elmesia to relax on a private resort island. Their brief vacation is interrupted by Yura, a shrine maiden from the underwater kingdom of Kaien who reaches the surface carrying an heirloom flute and a desperate request for help.

Kaien has long lived in peace under the protection of a sacred water dragon now trapped in deep slumber. Someone intends to awaken that guardian and turn its power against the surface world. Rimuru's group descends to the submerged kingdom, where a political conspiracy is tangled with the flute and a hidden power within Yura herself. Saving the azure sea means stopping an ancient protector from being transformed into the very disaster it once prevented.