Kuuenbu

"With the correct timing, higher and further jumps are possible while airborne. Kuuenzan may be activated while attacking in the air."

- In-game text

Kuuenbu or Kūenbu (空円舞), is one of the two special techniques that Zero learns after defeating Split Mushroom in Mega Man X4. This technique is based off Split Mushroom's ability to jump very high. This technique allows Zero to jump a second time in midair -- by pressing the Jump button a second time -- allowing him to jump even higher to gain access to otherwise out-of-reach areas (provided that the player does not dash-jump beforehand).

Trivia

 * It is possible that this "move" indirectly appears in Tatsunoko vs. Capcom, with the obvious reason of why Zero can double jump in the game.
 * However, in Marvel vs. Capcom 3, he oddly loses his ability to double jump as a balance measure from TvC.
 * From X4 onwards, Zero can use this attack and the Hienkyaku (mostly called air-dash) by default.