Nadia Cassel is one of the main characters found in both Metal Slug 4 and Metal Slug Defense. She's a member of S.P.A.R.R.O.W.S with private rank. From the French origin, Nadia is dreamed to be a supermodel, but couldn't resist the way of eating. She kept eating and increase her weight. So she enlists in the heroic Regular Army, despite her manager's plea to keep her weight down and succeeds in action.
However, Nadia finds the real potential for becoming a soldier and assigns into S.P.A.R.R.O.W.S to experience combat skills. The event against the Amadeus Syndicate is her first military training. When the event is all ended, she didn't like to leave her exciting life and inscribed into the secret military services of Regular Army to continue her job as the special agent.