Rapid is a new character introduced in Metal Slug Attack.
A Rebel Army officer in charge of their supply unit, Rapid is also the best train conductor in the Rebel Army, as no one is able to best her in steering trains. Her map route and schedules are also known for being impeccably accurate. She loves transporting supplies and the vehicles responsible for doing so.
While her military career is successful, her personal life is a mess due to a large number of gossips and secret admirers. If she is interested in someone, she will ask them if they would like to board her train.
First appearing in the Extra Ops "Supply Lines", she's informed by a soldier that Abigail has tasked her with disrupting the Regular Army's supply lines so she can defeat them in a decisive battle. Rapid spots Vita flying about and convinces her to help out with the task. Vita takes down a new model of the Regular Army's helicopter, though Rapid states that she prefers modesty. Despite this, she asks Vita if she would like to board her train as they depart back to base, where she gives Abigail a bill to cover the cost of the mission.
Later on in "Try Line 3rd", the Professor decides to attack a supply line with his new war machine, accompanied by the Gemini Twins. Rapid personally battles the two children with her new K-03 Coupled Armored Vehicle, angered by the fact that they decided to attack her supply lines. White is injured by the K-03, and the twins retreat upon spotting the Professor before Rapid can resume her attack.
Rapid appears in "We are the Mars People Rangers", where she is tasked with maintaining an Iron Cab when Abigail and Beatriz arrive to inspect it. Upon hearing of Martian invaders, Rapid offers her assistance to the two, though they refuse and tell her to hasten the Iron Cab's repairs so it can be deployed to assist them.