Okay, so here's our plot so far:
Muse A is the daughter of a pirate captain notorious for being ruthless and cruel. Muse B is the daughter of Calamity, Matron of the Dark Coven. It's Muse B's first chance to prove her worth to her Matron as she protects one of the outposts of the Dark Coven. An island where a powerful treasure lies.
Plot 1: The witches and the pirates battle over the powerful treasure (Excalibur, Sword of Light, which was stolen from the Light Coven), and Muse A's father is slain. Muse A and Muse B managed to put an end to the fighting, forge an alliance between the Dark Coven and the pirates. Therefore, Muse A becomes the new captain, and Muse B joins their team. Muse A can also wield Excalibur.
Plot 2: The mermaids learn Muse B has left her Matron's protection and Queen Ariel decided to exact her revenge. Muse B and Muse A are taken to the kingdom of the mermaids, learn of their plot, manage to escape using dark magic and try and convince as many pirates and as many covens as possible to band together (does not work well)
Plot 2.5: The Light Coven wants to wage war on the Dark Coven because Excalibur was stolen
*Excalibur has a twin named Clarent, which basically killed King Arthur and is kinda the 'Sword of Darkness' equivalent. We could do something with that
Pirates: Humans who sail across the seas, exploring islands and attempting to steal treasure from witches. They basically wage war against the witches, using their own creations—magical and enchanted treasures—against them, along with weapons forged by human hands. Weapons made of silver, which can slay any witch, guaranteed. Most pirates are known for cunning and ruthlessness, even attacking other human cities. There are many different renown captains out there, but none more so than XXX
Witches: Women with magical powers based around the elements. Each coven occupied several islands, whether they be guarding powerful magical treasures or living on their own turf. The most powerful coven is called the Dark Coven, renown for their dabbling in the shadow element. They are the most despised by the mermaids and the ones who have taken out the most pirates who try to steal their treasures. Witches create their own treasures using magic. Each coven is ruled by a Matron. There are eight covens (earth, air, fire, water, life, death, light & darkness).
Mermaids: Men and women—whether they be witches, pirates or humans—cursed by witches to live out their days underwater. No one knows the origin of this punishment, but witches curse people as punishment for crimes, for disloyalty or for money. Mermaids now bear a hatred for all who live on land while they are stuck beneath the waves. They are ruled by Queen Ariel (ehehehe), who holds a bitter resentment for the Matron of the Dark Coven, Calamity.