"Why the Mermaids Left Boralus" is a short story by Tamsyn Muir published in the anthology Folk & Fairy Tales of Azeroth. It is illustrated by Cory Godbey. The story tells of the relationship between the mermaid Halia and the tidesage Ery, and of how their love ended up saving the city of Boralus from a fierce storm early in its history.
The first part of the story establishes the setting, describing the still-new town of Boralus in the oldest days of Kul Tiras and the difficulties faced by its citizens due to the frequent and devastating storms and the lack of a seawall to protect them. This is followed by a description of the mermaids dwelling near Boralus and of how they undeservedly come to be seen as bringers of bad luck by the humans.
One young mermaid named Halia loves watching the human ships and becomes infatuated with Ery, a tidesage serving aboard the Windward, who in turn forbids her crew from killing the mermaid. When the Windward is anchored, Halia starts leaving gifts for Ery in Boralus Harbor. Ery is touched by this and becomes attracted to Halia's beauty as well, and during one voyage sharpens a knife so she can give it as a gift in return. Ery and Halia greet each other in the harbor, kiss, and confirm their feelings for each other. Halia tries to convince Ery to come live with her, claiming that the Mother will turn her into a mermaid if she slits her feet and walks into the harbor, but Ery refuses, citing her duties as a tidesage. They agree to keep their love a secret, since Ery would be rejected by her crew if they knew about the relationship.
They continue meeting in secret until a great storm comes to Boralus. It does not let up even after several days and threatens to destroy the town. Ery and the other tidesages travel to the river's mouth to try to divert the water, but they falter one by one until only Ery is left. Halia vows to help her beloved, and together they hold back a massive wave coming for the town. Ery states that their job is not yet done, and Halia decides to build a wall while Ery continues holding back the water. Halia's fellow mermaids join her in raising a wall from the seabed with mud and stone. The Windward arrives and tries to rescue Ery, but she does not come to them, and the crew instead witnesses her rising higher and higher above the water as the seawall is built up beneath her. Many of the mermaids die in the process, their power spent, but Halia returns over and over to ask Ery if the job is done yet. The tidesage eventually collapses from exhaustion and falls into the harbor. The waves crash into the wall, which holds steady. The crew bring Halia and the seemingly-dead Ery aboard. The mermaid slits her beloved's feet and then jumps back into the harbor with her. After a long wait, Ery surfaces, transformed into a mermaid and finally united with her beloved.
The story ends with a statement that all of Kul Tiras knows Ery's story and that its people now swear on mermaids as symbols of honor and sacrifice, since they were never seen in the harbor again after the storm. During certain sunsets when the red is reflected in the surface of the harbor, old sailors call it "Ery's blood", "in remembrance of the dutiful tidesage and the mermaid who loved her so faithfully".
- Great Sea