Guirail

Guirail (ギレール): an elite warrior from Nejirejia, Gurail was assigned by Evil Electro-King Javious I to assist Dr. Hinelar in his attempts to conquer the Earth. Sadistic and ruthless, Guirail's methods involved tactics that even his allies found reprehensible; such as kidnapping children to use as living shields and performing bizarre experiments on the Nezire Beasts. Among the powers he possessed included energy blasts, superhuman speed, and a dagger that could extend into a full length sword.

First appearing during a nighttime raid on the city, Guirail engaged the Megarangers where he used his speed to switch places with Megared's (Kenta Date) friend Takeshi, resulting in Takeshi taking the attack Kenta had intended for Guirail. Later, as Guirail attacked a major communications center, he attempted to manipulate Megared's guilt until a message from the recovered Takeshi restored Kenta's will to fight and Guirail retreated after receiving a firm thrashing from Megared's new Battle Riser.

With Neijirejia's tactics becoming more aggresive, Prof. Kubota and I.N.E.T. responded with the creation of a secondary mech, the Delta Mega, to backup Galaxy Mega. Gurail himself responded by enhancing Crocodile Nezire with the power to split into two upon recieving a fatal blow and sent him to deal with the Megarangers while he went after Delta Mega's chief programmer, attempting to force the scientist to surrender Delta Mega's command program by taking his son hostage. Again, Gurail was thwarted by MegaRed who was then able to activate Delta Mega to help the others deal with the dual Nejibeasts.

Giga Guirail
After repeated failures, Guirail and the others found themselves facing an enraged Javious who promised dire consequences if they didn't defeat the Megarangers soon. Knowing that his life was on the line as well, Guirail convinced Yugande to join forces and the two attacked a mining facility. But as soon as the Megarangers appeared to fight them, Guirial attacked Yugande from behind, weakening him enough for Guirail to merge with him into a composite form called Giga Guirail (ギガギレール, Giga Girēru?) . With Yugande's strength combined with his cunning, Giga Guirail froze MegaBlack, Yellow, and Pink in crystal blocks; then dealt a head injury to MegaBlue that afflicted Shun with amnesia and stripped him of all memory. After broadcasting a challenge over the city, Giga Guirail faced MegaRed and easily dominated him until Shun arrived to help and, after regaining his memory, worked with Megared to split Giga Guirail back into two beings. Refusing to accept surrender, Guirail combined with Yugande once again and grew giant, but was ultimately overwhelmed by the Megaranger's teamwork and separated just in time to use Yugande as a shield against Super Galaxy Mega's Super Galaxy Knuckle attack. Unknown to Guirail, a furious Dr. Hinelar had seen the whole thing and planned to enact a fitting retribution upon him.

Mad Guirail
Following his failure as Giga Guirail, Guirail was given the experimental NeziGen Capsule by Dr. Hinelar which had originally been intended for the now damaged Yugande, much to Shibolena's outrage. After luring out the Megarangers, Guirail swallowed the capsule and with its power surging through him easily bested all five Megarangers at once. Before he could deliver the killing blow however, Guirail's body began to mutate and he was forced to retreat. Confronted by Dr. Hinelar and Shibolena, Guirail was informed that although the NeziGen Capsule would increase his strength to unparalleled levels, the side effects would destroy his mind and warp his body. The two then abandoned Guirail as he transformed into a giant degenerate version of himself called Mad Guirail (マッドギレール) and began to rage across the city. Although the Megarangers attempted to stop him in Super Galaxy Mega, Mad Guirail's power and mindless fury proved too much for them to handle while even their new finisher, the Big Bang Attack, failed to inflict any signifigant damage. As Guirail's mutation resulted in him spawning the Nezi Beast Gigire from a piece of his own body, the Megarangers were forced to retreat in Delta Mega to the I.N.E.T. moonbase with Gigire in hot pursuit, leaving Mad Guirail to continue his assault on the now crippled Galaxy Mega. As Mad Guirail prepared to finish his opponent off, the Megarangers returned in time to save Prof. Kubota and the others with their latest weapon, the Mega Voyager. Against the Megarangers newest and most powerful mecha, Guirail had finally met his match and ultimately became the first opponent killed by Mega Voyager's Voyager Spartan attack.

But despite falling in battle, Guirail would continue to haunt the Megarangers even in death as Dr. Hinelar recovered the remains of Mad Guirail and used them to create a new breed of warrior for Nejiregia, the Psycho-Nezilar.

Gigire
During Mad Guirail's fight against Super Galaxy Mega, the power within him became too much for one body to hold, resulting in a piece of him breaking off and transforming into the Nezi Beast Gigire (ギギレ). As the two double teamed Super Galaxy Mega, the Megarangers were forced to retreat to I.N.E.T.'s moonbase in Delta Mega, only to find that Gigire was flying after them. After losing him in Earth's orbit and obtaining  the Voyager Machines from Yuusaku Hayakawa, the Megarangers faced Gigire again and managed to destroy him with the combined firepower of the Voyager Machines before combining into Mega Voyager to fight Mad Guirail.