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. Instead of working in the Syndicate's science army field, she resorted back to her original position as a mercenary for the Amadeus who leads the Pirates where she guards Amadeus territory across the seas; however, occasionally leaves her post in search for treasure.
She is good friends with Alma.
She keeps enjoying alcohol and sometimes drinks too much, even during the middle of a battle. However, her equipment has been customized so that even drunk her ability will not be impeded. 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.
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 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.