Four Guardians

Left to right:
Harpuia, Leviathan, Fefnir, and Phantom.

The Four Guardians, known as the Four Heavenly Kings (四天王) in Japan, is a group appearing in the Zero era. They are four powerful Reploids that were created from the DNA of X to help heal the planet's environment after the Elf Wars. They also serve in military capacities, leading the armies of Neo Arcadia. In the ZX era, all four return as Biometal.

In the Games

Zero era

Mega Man Zero

Left to right:
Harpuia, Leviathan, Fefnir, and Phantom.

The Four Guardians first appeared in Mega Man Zero, where they serve as four of the game's Mission bosses. They are:

• Sage Harpuia, leader of the Strong Air Battalion.
• Fairy Leviathan, leader of the Deep Sea Squadron.
• Fighting Fefnir, leader of the Scorched Earth Squadron
• Hidden Phantom, leader of the Cutting Shadow Squadron.

Once Zero begins turning the tide of the Resistance's conflict with Neo Arcadia, the Four Guardians target him directly. Zero fights and defeats them all in different Missions, forcing them to retreat.

In the Neo Arcadia Core stage, the Four Guardians return as part of the boss attack. They again retreat upon being defeated, save for Phantom, who self-destructs in hopes of taking Zero with him, though this fails. Harpuia, Leviathan, and Fefnir then appear before Copy X to defend him from Zero, but he orders them to stand down so he can fight Zero alone.

Mega Man Zero 2

The Guardians (now reduced to three) play a larger role in Mega Man Zero 2. With Copy X destroyed, Harpuia is forced to take his place and act as an interim leader for Neo Arcadia. The three continue to lead the Neo Arcadian military, though Phantom's Cutting Shadow Squadron is disbanded and its members are integrated into the other three battalions.

Elpizo's Operation Righteous Strike is brought to a halt by the Guardians, who destroy the invading force and corner Elpizo until Zero rescues him. While later pursuing the renegade Elpizo, Zero fights the Guardians across three missions. When Elpizo infiltrates the temples of Neo Arcadia, Leviathan and Fefnir both use their Armed Phenomenon forms to fight Zero again. Harpuia also fights using his Armed Phenomenon form, but only when Elpizo mind controls him using the Baby Elves. Though again defeated by Zero, all three of the remaining Guardians survive.

Mega Man Zero 3

The Guardians have a smaller role in Mega Man Zero 3. The three investigate the Derelict Spacecraft, only for Leviathan and Fefnir to be attacked and injured by Omega. Once Zero and Harpuia arrive, the fighting is stopped by the appearance of Dr. Weil and the rebuilt Copy X MK. II, who retakes control of Neo Arcadia from Harpuia. Subsequently, the Guardians are demoted and Dr. Weil replaces them as the leader of the military. While Leviathan and Fefnir stay in recovery, Harpuia grows dissatisfied and finally rebels against Weil after he orders an attack on a residential area. Harpuia then flees, finding asylum in the unlikely form of the Resistance.

In the Sub Arcadia stage, Zero can enter Cyberspace to find a secret boss battle with Phantom's posthumous data, who tests Zero's strength before encouraging him to face Omega. The drama tracks in Remastered Tracks Rockman Zero Telos reveal that Phantom went on to reunite with Cyber-elf X and rally the living Guardians to fight alongside Zero.

After Zero fights Omega, X and the three Guardians arrive to provide him backup. With their help, Zero lands a final blow on Omega, destroying him in a massive explosion. The fate of the Four Guardians afterwards is left ambiguous.

Mega Man Zero 4

Artwork from Vile's Incident.

The Four Guardians are absent from Mega Man Zero 4. A fan letter asking why was answered by developers in U-Capcom, explaining that the Guardians had disappeared and were working for the sake of the humans elsewhere. That same year, the Vile's Incident booklet from Remastered Tracks Rockman Zero Physis contained artwork of the Four Guardians and X watching the fall of Ragnarok, indicating they were still active (possibly as Cyber-elves, given the presences of Phantom and X). However, in the book Mega Man Zero Official Complete Works, Takuya Aizu claimed that this image was non-canon and that the Guardians died shielding Zero from Omega's explosion. Aizu later backpedaled in the book MM25: Mega Man & Mega Man X Official Complete Works, claiming that Neo Arcadia has no data on them but that they may be doing good for humans simply outside of Neo Arcadia's surveillance.

ZX era

Mega Man ZX

Left to right:
Model H, Model L, Model F, and Model P.

In Mega Man ZX, four Biometal based on the Four Guardians appear. Model H, Model L, Model F, and Model P (plus Model X and Model Z) were created by Ciel as a countermeasure to the evil Model W, meant to one day empower a righteous Mega Man so they could destroy it. However, these four Biometal fall into the hands of Serpent, who uses them to empower his Pseudoroids instead. Vent/Aile fights for the Biometal and Double Megamerges with them and Model X, accessing four forms: Model HX, Model LX, Model FX, and Model PX.

Mega Man ZX Advent

Left to right:
Aeolus, Thetis, Atlas, and Siarnaq.

In Mega Man ZX Advent, Prometheus and Pandora steal the four Biometal and deliver them to four new Mega Men: Aeolus for Model H, Thetis for Model L, Atlas for Model F, and Siarnaq for Model P. These four Mega Men are roped into the Game of Destiny, becoming pawns of Albert who seek to awaken Model W in order to supposedly become the Mega Man King. Grey/Ashe is able to copy their forms using Model A's A-Trans, making their four Biometal forms playable. These rival Mega Men are ultimately defeated, but still have their respective Biometal at the story's end.