Aileen is a new unit introduced in Metal Slug Attack.
She was a member of the Amadeus Syndicate but she joined up with the pirates because she couldn't stand military discipline, and wanted more freedom to act on her own. However, it is later revealed she left because she could not obtain the freedom she was looking for while in the syndicate. She became the leader of a group of Pirates, who would serve as Amadeus' mercenaries on the seas. She occasionally leaves her post to search for treasure.
She keeps enjoying alcohol and sometimes drinks too much, even during the middle of a battle. Despite the apparent clumsiness in her combat style, she is able to put up a good fight against hardened enemies. Her equipment has also been customized to work efficiently even if she is drunk. Because she aims to collect beautiful objects, she's off traveling the world in order to find rare gemstones.
First appearing in the Extra Ops "Break in the Shell", the Ptolemaics use the Emerald Turtle to find gemstones in the sand. Aileen hears of this and sets off with several pirates to steal the gems for herself. Upon arriving, she destroys the Emerald Turtle and claims the gemstones as her own.
Sometime afterwards, Aileen stumbles onto a large cache of treasure and decides to upgrade her and her crew's equipment, entrusting Wendy to perform the upgrades. Aileen herself obtains a new ride called the Iron Shark, and as she and her crew celebrate, they are joined in by Rillacle. The joyful mood is soon ruined with the appearance of zombies, and when Rillacle returns with a monster, Aileen realizes she is an Invader and orders her crew to fight the zombies while she personally deals with the monster herself. After a brief battle, Aileen and the female crew return to ship to party, leaving their male counterparts to fight the zombies off themselves.
When several Ptolemaic personnel boast about their successful gem treasure, Aileen overhears it and learns of the location after beating them up. She sets sail with her pirates, but she gets too drunk and falls overboard. When she regains consciousness, she finds a monkey with a gem and chases after it. Aileen soon runs into more Ptolemaic personnel and easily overwhelms them despite her clumsiness, eventually bumping into Red and his group. After following the monkey Asajiro to the gem zone, she reunites with her pirates, who were searching for her. They overwhelm the Emerald Turtle and set sail with all the plunder they could store. However, Aileen appears to have sleepwalked off her ship and is picked up by Red and his group.
Aileen eventually reunites with her pirates and hearing of Elysion's fabled treasure, decides to go after it. They break the seal that buried them, prompting Elysion and her crew to find and kill whoever disturbed their rest. During her mission, she scares Halle and a Mars People Pocket, who mistakenly believed her to be one of the ghost crew. Aileen and her crew soon engage Elysion and her own crew, with Aileen personally battling the cursed pirate, demanding her treasure. Elysion calls in a Ghost Shiee, though Halle and Pocket soon destroy it. This prompts Elysion to fade, disappointing Aileen as she wanted to take Elysion's treasure.
She later tries to help defend Red from a Ptolemaic Army assault by preventing as much landing craft from arriving. During the battle, she fights Damian, who destroys her ship in a magical explosion, but she survives the encounter.
- Aileen is the only limited Box Crank unit that doesn't use box items.
- She is the second Box Crank unit to have a Special Rare version. The First being was Navy.