The term "double jump" refers to the basic ability of jumping a second time while in the middle of an initial jump, without requiring the assistance of a solid object to stand on. This ability is a common feature in video games, and recurring in genres such as platforming and fighting games. In the latter it is usually given to fast and nimble characters with a small/normal body build.
Hiryu was given the Double Jump as one of his new mobility skills. At any point during a normal jump, Hiryu can perform a second jump which has him perform a rolling somersault in the direction held. This ability allows Hiryu not only to reach higher places, but also extend long jumps further and even switch directions mid-jump by holding the opposite direction. In low-gravity areas, Hiryu can also use the Double Jump to change the direction he's flying/falling away.
Hien also possess the Double Jump in his playable version. His boss version, on the other hand, possess the ability to perform unlimited air jumps. This was done in order to avoid him from falling off the Beraenavis during the Third Moon boss battle. If pushed off the mechanical serpent, Hien will constantly jump in mid-air until he can reach it back.Nang Pooh and Pei Pooh in Kazakh City's Residential District. Once obtained, Hiryu can perform a second jump in the air in order to clear obstacles such as the Perimeter Wall in the Military Ring.
Through the Plasma Capacitors installed on his boots, Hiryu releases a burst of concentrated plasma energy which propels him upward, allowing him to perform a second jump while still in the air. This ability has no offensive use, and is used primarily to clear obstacles and large pits. It can also be used in combination with the Plasma Catapult in order to reach places and items outside the range of either skill.