Fourth Armor

The Fourth Armor (フォースアーマー), sometimes referred to as the Force Armor, is an all-around armor first found in Mega Man X4. In its debut game, it it was collected in four parts and slowly became more powerful as the parts were collected, similar to armors found in the previous games.

After the events of Mega Man X4, an imperfect reconstruction of this armor created by Alia can also be used in Mega Man X5. If X is chosen at the Character Select screen at the start of a new game, he will begin the game with the armor equipped, and it will be available for the rest of the game. The second Arm Capsule ability is in effect, enabling the Plasma Shot, but the effects of the Helmet Part are disabled for the duration of the game. The Nova Strike is also unavailable. If Zero is chosen instead, the armor will become damaged in the first stage and the armor becomes unavailable for the rest of the game.

Functions

 * Head Parts: Increases X's special weapons capacity, allowing him to fire endless uncharged special weapons. In Mega Man X5, this is reduced to a 50% energy consumption reduction. It should be noted that this 50% reduction effect becomes the standard helmet function from Mega Man X5 onward.
 * Body Parts: Allows X to use a Giga Attack, the Nova Strike. It is a rushing, invincible, damage-inducing attack, with limited energy that is restored over time. Also, the damage X receives is halved, and taken damage is absorbed to replenish the Nova Strike's energy. This armor's Giga Attack is only available in Mega Man X4.
 * Arm Parts: These upgrade X's arms, changing his standard charge shot, while allowing him to charge weapons.
 * Stock Charge Shot: Allows X to charge up four charged shots at once. Four icons of plasma will appear next to X's life gauge that are used to keep track of the number of X's shots. Whenever X fires while an icon is visible, he will fire a charged shot. The equipped parts will have white arms and blue fists. The only drawback to this part is that the charged shots are smaller in size.
 * Plasma Charge Shot: Upgrades X's charged shots to the Plasma Shot. This shot is much larger and more powerful than the standard blast, and will leave up to three plasma balls generated and causes continuous damage. In Mega Man X5, this is the Arm Part X keeps, but it is weakened to leaving only 1 plasma ball behind per shot and the shot can not pass through walls. However, unlike in Mega Man X5, the Plasma Shot is quite useful against bosses. The equipped parts will have black arms and red fists, however the X5 version will have the colors used for the Stock Charge Shot which fires the Plasma Shot for graphic consistency in that game. The main drawback to this part is that the plasma balls left behind will take priority in dealing damage, meaning that if X fires a charged shot and then use a semi charged shot or special weapon afterwards, the damage will be cancelled due to the plasma ball already dealing damage.
 * Foot Parts: X can air-dash and hover by double-jumping. He can move while hovering, but the amount of time he will stay airborne is reduced. This the only Fourth Armor's part that still retains its full ability in Mega Man X5.

Locations

 * Helmet Part: In Cyber Peacock's stage. If the player completes the third section in the first part of the level fast enough to receive an S rating, the Helmet Capsule will appear in the next area.
 * Body Part: In Magma Dragoon's stage. Found in a passage above and to the right of where the Ride Armor is found. It is reached by dash-jumping in the Ride Armor from the highest point and ejecting from it in mid-air. You will need one of the Arm Parts and Twin Slasher to destroy the blocks that stand before the capsule. Enter the passage to find the Body Capsule.
 * Arm Part: In Storm Owl's stage. In the second part of the stage, right before the laser-based miniboss, there is a spike-lined vertical passage. To reach the top, fire a Lightning Web right in front of one of the spiky walls and use it to ascend the passage. At the top, there are two capsules that the player can choose. The player may return to these capsules at any time and switch Arm Parts as desired. In addition, if timed at the correct position, using the charged Rising Fire while in mid-air can make it easier to ascend the passage during return visits without having to worry about the spikes.
 * Capsule 1: The closest capsule upgrades X's charged shots to the Stock Charge Shot.
 * Capsule 2: The farthest capsule upgrades X's charged shots to the Plasma Charge Shot.
 * Leg Part: In Web Spider's stage. Keep to the right throughout the beginning of the stage. There will be a break in the wall, and the Leg Capsule will be within it.

Rockman X4 manga
The Fourth Armor made an appearance in the manga version of Mega Man X4. After a bruising fight for his life against rogue Repliforce soldier Frost Walrus where X barely escaped with his life thanks to the General's timely intervention, X decided that he needed more power to defeat the Repliforce and stop their coup d'etat. So he decided to return to the Kagikira Forest where he had earlier defeated Web Spider of the Repliforce Guerrilla Unit and obtained the Ultimate Armor from Dr. Light's hidden capsule there. Although, Light warned him that the armor's power could be a double-edged sword and deeply affect him in unforeseen ways. Thus, X becomes a much more powerful and ruthless warrior.

With the power of the Ultimate Armor, X single-handedly defeats remaining Repliforce sub-commanders Slash Beast and Storm Owl, and is able to defeat the power-hungry Maverick Magma Dragoon as well at a volcano after being ambushed there. Then, X ventures to the Repliforce space station Final Weapon that holds a "Death Flower" weapon capable of decimating the entire planet with a single blast and confronts the General, severely wounding him in combat and knocking him out. But suddenly, Repliforce's deadly weapon is activated by a mysterious yellow Maverick who X had previously encountered at an abandoned laboratory.

X then engages the Maverick in battle, who reveals himself to be none other than Double, X's loyal subordinate. Double than slashes at X wildly and injures him, but he quickly recovers thanks to the Ultimate Armor and smashes right through Double with a Nova Strike, furious with his treachery. Double's body disintegrates. General then rises up behind X who frantically shoots at him with buster shots that do not damage him, but instead of killing X the General hugs him, and then sacrifices himself by slamming his own body into the Death Flower and destroying it.

The explosion reaches X and the force from it causes his Ultimate Armor to explode, which reveals the Fourth Armor that had been hidden underneath it the entire time. X reunites with Zero and they decide to return to Earth, with the war being over and the Earth being saved.

Trivia

 * The armor is actually unnamed in Mega Man X4, as armor naming did not begin until Mega Man X5. As such, the Mega Man X4 armor has no name, just like its predecessors, simply being referred to as the "X4 Armor".
 * The armor is called "Fourth Armor" within X5 's menus.
 * The armor is often called the "Force Armor" in some sources. This is a misunderstanding however, as the Japanese word "fōsu (フォース)" can be easily misinterpreted to mean "force" when viewed out of context.
 * Notably, fans also refer to the armor as "Nova Armor", due to its Nova Strike Giga Attack.
 * In Mega Man X4, the colors of the Arm Parts for the armor are different when equipped with either the Stock Shot or the Plasma Shot in order to distinguish the two. For the Stock Shot, the forearms are white and the hands are blue, matching the original design of the armor (also to the fact that the buster features four small barrels). For the Plasma Shot, however, the forearms are black with yellow wrists and the hands are red.
 * In Mega Man X5, however, the completed Fourth Armor's Arm Parts are white-and-blue and the type of shot that is built-in is the Plasma Shot. This change on the original buster function could be applied to the fact X5 added two new armors, making the total count of usable armors for X to 5 (If his Unarmored form is in count). So they decided to reuse Ultimate Armor's plasma shot in X5 to save some space in the memory and making the buster shot weaker in exchange.
 * Since the Ultimate Armor is the most recurring armor in the series (and the fact that it is essentially an upgrade to the Fourth Armor), most of the Fourth Armor's abilities (Plasma Shot, Nova Strike and Hover) are also the most recurring abilities in the series.
 * In the manga adaptation of Mega Man X4, the Fouth Armor is not used during the Repliforce conflict. X instead discovers the fully formed Ultimate Armor, which he equips and uses in a blind rage against the Repliforce after suffering a mental breakdown. After General's sacrifice, the resulting explosion destroys the Ultimate Armor while protecting X, revealing the pristine Fourth Armor underneath. As Sigma and the Repliforce have already been defeated, the abilities of the Fourth Armor are not explored in the story.
 * Archie Comics writer Ian Flynn admits that he did want to have X go Super while in this armor in Worlds Unite, but Sega wouldn't let him do it.