Blacksail
Interact with the Plane Anchor, defeat the Void Pirate, and reveal the Void Sea Seal to obtain a Seal Whisper.
With 6 Seal Whispers, you can go to the Void Sea Terminal and defeat the Void Sea Bride to obtain rewards.
Monsters with Void Sea Flames will appear when the stage is "marked by a Plane Anchor". Defeat these monsters to get Void Sea Flames. Void Sea Flames come with various effects, such as granting extra drops or changing subsequent Seal Whispers.
After you defeat a stage boss, a Plane Anchor will appear. You can interact with the Plane Anchor and defeat the Void Pirate to reveal a Void Sea Seal and get a Seal Whisper. Seal Whispers include Whisper of Armament, Whisper of Wealth, and Whisper of Wonder. These Whispers will greatly affect the final rewards.
With 6 Seal Whispers, you can go to the Void Sea Terminal to defeat the Void Sea Bride and get the rewards in the Treasure Chest.