- "I have absorbed Schmitt! My name is X, Doppler's most powerful warrior!!"
- —"iX", Rockman X Mega Mission card no. 34
X (イクス Ikusu, pronounced "iks"), referred as "iX" among fans, to differ him from the original X (エックス Ekkusu, pronounced "eks"), is an evil Limited doppelganger of the original Mega Man X, introduced in the Rockman X Mega Mission series. "X" makes a comeback in Mega Mission 3, as Return X (リターンイクス Ritān Ikusu), RX (Rイクス) for short. He returns yet again in Rockman X Mega Mission 4 as Grow X (グロウイクス Gurou Ikusu), GX (Gイクス G Ikusu) for short.
In his original form, "X" bears a strong resemblance to the original X. However, he is easily distinguished by the different color scheme, having a green body instead of blue. He also stands out for the round gem on his helmet surrounded by four spike-like marks, a common feature on various Limited Reploids. Thunderbolt streaks running across his cheeks, spiked guards around his wrists and ankles as well as steel joints for his elbows and knees. The decorations on his helmet and chest plate are dark purple as opposed to light blue, and his eyes are red. In the Rockman X Mega Mission manga, "X" also features a spiked collar and two spikes on his back.
"X" appears to have the same abilities as the original, albeit significantly enhanced by the Limited in his body; has the techniques of all Reploids revived by the Limited, he is shown to be an extremely tough opponent for the real X, who only manages to fight back due to the Clear Armor generated by the Limited he had absorbed.
In his introduction, "X" claims to be Doppler's strongest warrior, indicating a bold and confident personality with no association to Sigma. The cards convey him as an aggressive and ruthless fighter, going all out against the real X from the start. Whereas X uses an informal, masculine Japanese speech style, "X" is gender neutral and formal to show he does not share the original's personality quirks. While the Limited have displayed fear and self-preservation instincts, "X"'s birth is referred to as when they gained a will of their own. He may be single-minded in his original directive to evolve beyond and destroy X, but his desire to fulfill the goal on his own terms causes "X" to act in more complex ways, including self sacrifice.
As Return X
"X" experienced drastic physical changes since his defeat against X; his armor now has a more snakelike appearance, with long and curved surfaces complemented by intricate detailing on his arms and chest, the latter vaguely resembling a sinister face with red crystals resembling eyes.
In his new form, named Return X, is shown to be extremely powerful, as he is capable of single-handedly repelling the Hyper Limited Mavericks that X and Zero struggled against in the story. He is revealed to have the power of shapeshifting, as he can liquify his form and even split himself in two, taking the form of powerful armor upon merging with the two Hunters. He also has the ability to regenerate as long as his core remains intact.
Return X has grown much more determined after his defeat, being able to resurrect himself by sheer force of will. He is completely obsessed with defeating the original X, to the point of turning against the Hyper Limited Mavericks and even lend his power to X and Zero to destroy the opposition.
Rockman X Mega Mission
The Limited version of X is born when a defeated Schmitt retreats in the hopes of having his body regenerated by the Mother Limited. However, the Mother Limited instead absorbs Schmitt and absorbing data from the bodies of the Reploids defeated by X and Zero, uses all the data gathered on Mega Man X to create the Limited copy. Claiming to be the strongest, "X" nearly overwhelms the original, even as the Limited leaked in the fight produces the Clear Armor around X's body. Struggling against the influence of Limited, the original engages the copy in a final attack, both firing their busters at each other's chests; when it seemed that mutual destruction was assured, X allows the copy's attack to obliterate the Clear Armor (and thus the Limited in his body) before escaping at the last second. The fake is defeated.
Rockman X Mega Mission 3: Versus Hyper Limited
"X" makes his comeback suddenly as X and Zero fight the four Hyper Limited Mavericks wreaking havoc in the Maverick Hunter HQ. Now calling himself Return X, with his power increased, he defeated the Mavericks so nothing would disturb his fight against X, claiming that he will defeat X himself. However, just as Return X prepares to deal the final blow, he is shot from behind by the Order Breaker Enemice-HL, who questions Return X's betrayal. Not wanting to share the battle with Enemice, enraged by the intervention, Return X launches an assault against Enemice, but eventually decides to assist X and Zero against him, taking a liquid-like form and splitting into two to merge with X and Zero, becoming the EX Armor ("iX" Armor) to defeat Enemice HL.
In response, Enemice summons the four Hyper Limited Mavericks and uses a special chip to combine them into Mix-Forte, but Mix-Forte is destroyed by the Hunters, who then defeat and corner Enemice. Desperate, Enemice activates the Sigma Chip in an attempt to obtain Sigma's power, but is instead consumed by Sigma's program, becoming Sigma Limited. Zero, attempting to take him on alone, is defeated, causing his portion of Return X's power to recombine with X's half, creating the All X Armor. With this new power, X defeats Sigma Limited with the Double X Buster attack, and the All X Armor melts away as Return X converted his own body to energy for X to fire. However, X doubts that he has seen the last of Return X, having a premonition of him biding his time, reviving in secret, having absorbed the abilities of the Sigma chip from the scarce remains of Sigma Limited.
In Hitoshi Ariga's manga Rockman Remix, there is a chapter dedicated to the first Mega Mission. When X defeats Wire Sponge Limited, the Limited within the revived Maverick leaps from its host's body, in an attempt to infiltrate X. Zero arrives in time to destroy the core of the Replibrain with his Buster, but the bio organic slime from it still splatters on X's buster, infiltrating X and causing him to pass out from pain. While he is unconscious, an alter ego within him with "X"'s appearance appears, claiming to be X's "power", and promises X incredible strength if they were to merge.
When X wakes up, his X-Buster has mutated into the Clear Buster, and seemingly in a trance he attacks Zero, who sees a strange shadow behind X (the alter ego). Throughout the story, X is periodically possessed by his alter ego, becoming a mindless killer who attacks anyone in sight. During the fight against Schmitt, Zero says to X that the soul is more important than the strength, which is useless without feelings, giving X a better control over his body. When X defeats Schmitt, he is absorbed by the Limited, forming "X"'s Limited double, who catches both X and Zero off guard, shooting Zero from behind, enraging X and allowing his alter ego to take control, the Clear Armor forming around his body.
"X" taunts the enraged original with comments on how if power is what makes a Hunter, then he could be a Hunter too. The damaged Zero intervenes in the battle, standing between X and the copy. X, enraged and under the influence of the Limited within him, the alter ego manages to increase his control over his body, evolving X's High Clear Buster to the Clear Armor and fighting against "X", threatens to shoot through Zero. Zero however, reminds X that the heart is what counts. X appears unfazed and shoots, but his shot goes over Zero's shoulder, barely grazing him, and strikes the double directly, defeating him and completely dispelling X's limited infection, along with it the Clear Armor and his alter ego. The defeated "X" is then absorbed back into Doppler's giant Limited to form the Mother Limited, evolving it to the Repligigant Mother Limited.
Mega Armor series
His Return X form has a model figure based on him in Bandai's Mega Armor series of models. The original release featured only the armor, molded in transparant green plastic, in a plastic bag, but was later released with a body to mount the armor onto on its own. This figure was re-released several years later along with a new metallic plastic version. Due to sharing parts with other figues, the included face does not feature Return X's red eyes or yellow cheek streaks.
The EX Armors of X and Zero and the All X Armor were also made, with the EX Armors originally being released as add-on parts for the X and Zero model kits with individual releases years later, and the All X armor having its own figure release. Both models were released in transparent and plated variants.
- "X" is the only character exclusive of the Mega Mission series to have a model figure, however only for his second form, Return X.
- The Return X model kit, along with art created for the model's rerelease, display his armor as being transcluscent similar to the Ultimate Armor. This effect is not seen in the original Megamissions art however.
- "X" is the second antagonistic clone of X, being X-Kai the first one chronologicaly and Copy X being the last.