The Jet is one of the unused sprites found in Metal Slug 5. Not much is known about this vehicle. Metal Slug fans claim that the pilot of the Jet is Rumi Aikawa, however that is unlikely because of the many differences in facial features. Whether it was intended as a playable slug, a support unit that assists the players in combat, or just a background element on Mission 2's flying section, is unknown.
The Jet is modeled after the German Messerschmitt Me 163 Komet.
Of note is the fact that it doesn't have a Vulcan, so instead of a playable Slug, it could have been designed as an enemy vehicle from the Rebel army (with the possibility of it having been hijacked by the player) or intended to appear in a cut scene.