The Melusine Pirates was founded by a young half-dagon named Meiru. While living in the outlaw city of Andika, Meiru's mother Reej was taken from her by Baharl Devault. Meiru was then living in the slums until she was adopted by her now first mate Chris. The two of them managed to gather more comrades until they eventually assembled a pirate crew. As Meiru was recognized as the leader, they decided to name themselves after her surname, as per pirate traditions. Due to her dagon heritage, however, Meiru did not have a surname, and so decided to give give herself the name "Melusine" (which meant Master of the Stormy Seas).
Theeir objective was to take over Andika and free it from Baharl's control, but Meiru's true goal was to reunite with her younger half-sister Diene Devault. In order to achieve this, they would battle other pirates, capture them and convince them to join their crew after Meiru tortured them with her Ancient Magic until she had amassed a crew of over 500 (many of whom were refugees that left Andika). This earned them the reputation of being a ghost ship after they rescued and returned the other pirates' captives and mysteriously disappeared in a blanket of mist soon afterwords.
During one of their attacks, they were confronted by the Liberators Miledi Reisen and Oscar Orcus, who were chasing after other pirates that raided Andika. After an intense battle, the two sides ceased fighting after Meiru accidentally caused grave injuries to Miledi and offered to heal her. After both sides introduced themselves, they were suddenly attacked by giant aquatic monster that was drawn to them by the large amounts of mana that was used during the battle. The pirates decided to abandon Miledi and Oscar and escape the monster. Even so, the two Liberators defeated it and rendezvous with the help of their comrade Naiz Gruen Caliente. Miledi and the others spent the next month living with the pirates at their secret base and becoming good friends with each other, as well as trying to convince Meiru to join the Liberators due to her being in possession of Ancient Magic. Despite Miledi's efforts, Meiru refused her offer due to her goal of wanting to rescue her sister. Miledi and the other Liberators left them upon learning of Meiru's motives. Soon afterwards, the pirates where attacked by the Holy Church's templar knights due to the rumors spreading of Meiru as the "Saint of the Western Seas". They managed to hold their own against the knights thanks in part to the Artifacts that Oscar made for them during his visit, but they still took casualties. As Meiru was battling the templar knight's commander Laus Barn, she was about to be killed, but was saved by the timely return of Miledi and the other Liberators. The knights were forced to retreat after having lost 30 percent of their forces. Despite their victory, however, 57 of the pirates were also killed. Meiru decided to meet with Laus in order to convince him and his knights to support her plan to take over Andika since the Holy Church was secretly controlling the island city. Laus agreed after Meiru convinced him that she was more valuable than Baharl as someone they could control, but he had to report it to church before they could help her. The church agreed to aid her, but only after they would be allowed to take Diene into their custody due to her being a Atavist. As a result, Meiru and the pirates decided to infiltrate the city in order to rescue Diene before the church could get her. They attempted to rescue Diene by having Meiru and Naiz reach her hidden chamber, but after seeing that she was taken away by her father, the pirates and Liberators caused a riot throughout the island in order to distract Baharl's security forces long enough to rescue Diene. Unfortunalty, the templar knights arrived soon after and once again attacked the pirates due to them ignoring the original plan to wait to invade. Miledi and Oscar managed to hold back the knights and inflict serious casualties on them. As the battle raged on, however, a much larger threat appeared. A giant monster known as the "Divine Beast Leviathan" had awoken from its seal and began to attack Andika. It was eventually killed due to the combined efforts of Meiru and the Liberators, but Andika had sunk as a result of its release (though all of its citizens were reduced by Naiz). The knights retreated after having been reduced to one fifth of their original force from the battle. The pirates then helped relocate Andika's citizens by assembling the wrecks of sunken ships that were restored by Meiru's magic. After a month of building a new home for the people of Andika, many of them decided to join the Liberators after having witnessed Miledi fight to protect them. The pirates said their goodbyes to their allies and took off to explore the ocean, but Meiru decided to join the Liberators after she had bonded with Miledi, to which her comrades happily supported.
The pirates would later rescue Aisha after she and her two bodyguards, Failur and Scardy, were stranded at sea while trying to find Oscar, and took them to Andika (or rather the new land of outlaws due to the island having been sunk). Aisha learned about the pirate's relation with Oscar and also bothered Kyaty Cougan, after finding out that Oscar saw her in a maid outfit.