The Empress Siren, also known as the Seventh Siren and the Queen of the Seven Seas during her final phase, is the leader of the Seven Sirens, making her first appearance in the final area, is also the oldest, and the final boss of Shantae and the Seven Sirens. Before the events of the game, she was defeated by the Guardian Genie who stripped her of her powers. Only by absorbing Risky Boots and the Half-Genies was she able to mostly regain what she lost upon her first defeat. She required the power of 5 Half-Genies in order to become truly invincible. However, Risky Boots sabotaged her plans by having RottyTops take Shantae's place as a fail-safe.
The Empress Siren is even worse than Risky Boots is. While Risky Boots just wants all the treasure she can find, the Empress Siren is willing to go to great lengths to get her prizes.
During her first phase, the Empress Siren teleports around the stage, blowing harmful bubbles and tossing two blades. She can also send electrical shocks.
The second phase is vastly different. The arena grows so huge you cannot see it entirely, and the Empress Siren herself grows even bigger than the stage. During this phase, she has 24 weak points and attacks by throwing lightning balls. When the Empress Siren falls, the game is completed and the Half-Genies whose power had been absorbed go free, as does Rottytops (who got captured as well).
- Out of the Seven Sirens, the Empress Siren, Lobster Siren, and Coral Siren are the only ones to have functional humanoid legs.
- She's also the only siren in the group that has actual conversation dialogue. While Lobester Siren does interact, she only communicates with sounds. The remaining sirens act as bosses that do not interact with Shantae.
- She becomes the largest final boss to be encountered in the entire franchise, growing about 5 to 8 times larger than the Tinkerbrain.