The Charge Mode is a special mode in which Hiryu's abilities are enhanced for a brief period of time. In order to activate this mode, Hiryu needs to perform a long, continous chain of strikes against enemies until it fills out the "Charge Strike Meter" (a circular red meter with Hiryu's "Hi" kanji in its center, found left of the health bar). The strikes don't need to be against the same enemy and as long as Hiryu is not struck or takes too much time to continue attacking, the meter will keep building up.
When Charge Mode is active, Hiryu's body is engulfed in white plasma energy and all enemies on screen appear glowing red. In this mode Hiryu's attacks are in a perpetual charged state, and for its duration they have double strength and range. Hiryu also perceives everything around him in slow motion, making attacking enemies on his proximity much easier. This power-up state lasts around 5 seconds, but it can be re-initiated again as soon as the Charge Strike Meter is filled up.