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.
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 gem stones.