Constellation System

The Constellation System is a line of five separate machines that are compatible with each other, created for military use by the Square Islands. However, given the fact that Sq. Isles is a secluded area with a bunch of nerds working on insane projects that no sane country cares about annexing (partially due to indifference, partially due to fear of Area 70), each of the mechanical beasts were distributed to trusted countries of the UAN, specifically the USA, Castilla, UnitedTerra, Shops Island, and Francterre.

History
The Constellation System began as a project created by a couple of Sq. Isles employees who had clearly watched too much of those shows with spandex fighters and giant robots or something. However, as the idea progressed, the higher-ups at the facility decided that they could use the Constellation System to boost their legitimacy as a country by building each machine for military purposes instead of creating like another five Hero Mechas on top of the three that were already being made.

On October 10th, 2015, the Sq. Isles announced the system's creation, raising the country's approval ratings significantly. The recipients were chosen to be the USA, Castilla, UnitedTerra, Shops Island, and Francterre, the five main powers of the UAN (though the latter was later replaced).

The designers wanted to create a cross-combining system that would allow any two countries that had a mech from the Constellation System to form a superrobot that could defeat enemies with ease, but were unable to figure out how to make the system work without individual parts that were far too complex to be practical, as taking too long to form the robot in the middle of a battle would leave a serious opening. Thus, the team opted to instead remove one of the machines from the combination system, making it able to become a robot on its own, and create two top-half machines and two bottom-half machines. This would mean that all but two combinations of Consellation alliances would provide a single robot to work with.

To top that off, to commemorate any special occasion where all five units were in one place, Sq. Isles developed a super-combination that would be able to plow through enemy forces to make sure wars didn't last too long (relatively speaking) so as to interrupt other stuff: the Infinity Constellation. Their idea was that if any situation arose where all five owners of Constellation mechs had to pour their resources into war, the opponent must be notably strong, and thus the Infinity Constellation would need to be used. Whether Infinity will stand the test of combat will have to be seen.

Taurus, Scorpio, Aries, and Leo were completed on May 5th, July 4th, October 31st, and December 25th of 2016 respectively, Ursa was completed on July 4th, 2017, and development for Infinity was finished on July 13th, 2018, at which point the machines were finally distributed.

Scramble for Power
The system is heavily reliant on its users' status with each other to function with maximum efficiency; therefore, the Scramble for Power in 2027 resulted in a climactic situation involving Castilla, Francterre, and Shops.

Castilla and Francterre briefly joined forces using Eclipse to fend off the Snoss from Northern Shops; this battle resulted in a deadlock as Eclipse was pitted against the Snoss's superior firepower. While this was happening, the rest of Francterre's army conquered the mainland; Francterre then forcibly split the combination and used Leo to force both Castilla and Snowzerland out. Taurus and Leo did not engage as the Constellation System's failsafe feature prevented either of them from attacking each other, so Francterre worked around this by attacking everything else.

After this event, both Taurus and Leo were used to forcibly break through the defenses of both sovereign nations and former Shops colonies; with the faltering structure of Shops's military, Aries was unable to provide much support in the way of defense. It was finally able to join a battle and seemed to provide some resistance, but ultimately succumbed to ballistic missile fire.

The USA and UnitedTerra did not intervene; even if they wanted to, neither Ursa nor Scorpio could do much against the rampaging Taurus and Leo due to the failsafe.

Once the whole fiasco was over, the Square Islands recovered Aries and began repairs, trying to figure out a different nation to send it to. Most of the workers did not approve of the "mechanical power abuse" that Castilla and Francterre showed, and went to work designing a lockdown system that would prevent the machines from being used for "unfair annexation".

The eventual solution was to have a master control panel in Shops Island that would shut down any of the Constellation units should they cause chaos in weaker countries. Aries was sent to Amataria, partially due to their robotic expertise, and partially as kind of a cathartic joke for Amataria since Shops often condemned their fascist government.

Ursa
The Ursa unit is the USA's Constellation machine, based on a bear. Unlike the rest of the Constellation machines, it has its own robot mode and is arguably the strongest of the five, fitting for the USA. In its bear mode, it is best used to swipe at enemies with its giant paws, while in robot mode, it can focus on "more sophisticated" combat. Y'know, if "more sophisticated" meant goin' ham and punching stuff in the face.

Taurus
The Taurus unit is Castilla's Constellation machine, based on a bull. Fittingly for a bull, it can rampage through rows of tanks with ease, but it also has lightning shots and a cannon for some more explosive combat. The downside is that it uses a lot of power, and Castilla is currently working on trying to either overcome or work around this issue.

Taurus is a "lower-half" Constellation, forming the legs for Hurricane and Eclipse.

Scorpio
The Scorpio unit is UnitedTerra's Constellation machine, based on a scorpion. Its main gimmick is its high defensive capabilities, able to generate force fields to protect itself and its fellow troops. It can also fire its claws to grab enemy air machines, or for grappling hook purposes if anything strong enough to hold it can be found. For offensive attacks, Scorpio must get up close and strike enemy machines with its stinger, draining energy and (relatively) peacefully disarming enemy forces.

Scorpio is an "upper-half" Constellation, forming the body and arms for Hurricane and Ghost.

Aries
The Aries unit is Shops Island's Constellation machine, based on a goat. Its high maneuverability allows it to circumvent enemy blockades, and its attacks are precision-based, directly knocking out important machinery, such as main engines or reactor cores. Unfortunately, this requires expert control to use properly; some have suggested that Shops Island reactivate some of their SIA Drones specifically for Aries control purposes.

In the future, after the end of Shops's reign, Aries is recovered and transferred to Amataria, which will hopefully use it for defensive purposes and not world domination or waffle raids or something.

Aries is a "lower-half" Constellation, forming the legs for Aero and Ghost.

Leo
The Leo unit is Francterre's Constellation machine, based on a lion. Its high speed stat allows it to rush into battle, guns blazing - or, in this case, mouth blazing, because its primary weapon is its fire blast that it unleashes from its mouth, scorching tanks and other stuff like that. It also has a wipeout attack that summons a bunch of energy lions that all charge at the enemy.

Leo is an "upper-half" Constellation, forming the body and arms for Aero and Eclipse.

Combiners
Although each of the machines are powerful enough to fend off entire armies on their own, they really shine when they start working together, forming mechanical powerhouses. If an "upper-half" and "lower-half" unit are on the same side during a war, they can combine and start causing rampant destruction everywhere, booyah!!

Hurricane
The Hurricane combination combines Scorpio and Taurus, symbolizing the union of UnitedTerra and Castilla. Its primary weapon is its supercharged shoulder-mounted long-range energy cannon (whew), which can fire energy spheres that erupt with unprecedented force upon impact. Randomly launching energy spheres everywhere is just begging for collateral damage, though, so Hurricane is also equipped with a special projectile that deploys a bubble barrier when fired. Trapping an energy sphere and its victims in the barrier decreases outward damage while increasing the explosive power by altering the explosion's density.

Aero
The Aero combination combines Leo and Aries, symbolizing the union of Francterre and Shops Island. It is designed for aerial combat with its jet boosters, allowing it to fight both armies and air forces simultaneously. Aero's primary weapons are the two large sets of missile launchers on its torso, though it also retains Leo's fire blast attack.

Ghost
The Ghost combination combines Aries and Scorpio, symbolizing the union of Shops Island and UnitedTerra. It is loaded with various explosives and gadgets to chuck directly into enemy forces. Of those, the gravity field and bomb roulette are used the most; the former is activated by a top-shaped projectile that pulls in anything in a set radius, while the latter tosses a cube containing a random explosive that the system specifically chooses for the given situation.

Eclipse
The Eclipse combination combines Taurus and Leo, symbolizing the union of Castilla and Francterre. It's a glass cannon that moves at a speed that shouldn't even be possible; in fact, it even has a time-distortion skill that slows time for everything around it for a brief period of time, allowing it to do just about whatever it wants. Eclipse's main combat weapon is its electric bursts, which have shocking effects.

Infinity
The Infinity Constellation, also known as Infinity, Voltron(?!), The Hammer of Death, and YOU'RE ALL DEAD, is the combined form of all five Constellation units, symbolizing the union of all five countries. It's not the fastest thing in the world, but it brushes off most attacks with ease and has a giant stinkin' hammer that wrecks just about everything in a 5-kilometer radius!! Quite frankly, the development team probably could've (and definitely should've!!) stopped there, but instead they decided to give it the ability to drop a humongous cannon  from the sky and blast everything to pieces!! Let's just say there was a reason why development of the Constellation System took so long after Leo. Clearly, the EPF did not want another Frosian War.

If in any case a country finds themselves opposed by the USA, Castilla, UnitedTerra, Shops Island, and Francterre all at the same time, it is highly advised that they just surrender at this point. Quite frankly, some people want to see anyone try to stand in the way of Infinity, just to see it in action.

USA
"OH YEAH! WE HAVE A GIANT MECHANICAL BEAR THAT TURNS INTO A ROBOT! COME AT US, SNOWZERLAND! HOW DO YA LIKE US NOW, NORTH JOSEON?!"

- An excited USA soldier in an interview

Simply put, the USA was ecstatic and invited Ursa with open arms, perfectly willing to add to their already uber-OP military force.

Castilla
Castilla was pretty happy about Taurus, and are hoping to figure out how to use its firepower to counter potential nuclear threats.

UnitedTerra
Despite their powerful military, UnitedTerra is still generally considered an inactive force, though they state that they'll be putting Scorpio to good use. A UF officer has expressed concern that UTR will be dragged into several conflicts just so that the other four countries can have Infinity on their side.

Shops Island
Some citizens questioned why Aries's secondary color was pink, instead of a color that would've made more sense, like lavender or something. Sq. Isles responded by stating that they had conversed with key Shops personnel and decided to create Aries the way they did because it was "strategically... adorable."

Francterre
Francterre is generally satisfied with Leo; some soldiers have expressed their hopes that it will help them rise the military ladder, especially considering Francterre is ranked the lowest among the five users of Constellation machines.

Other

 * Square Islands had a massive party to commemorate the machines' completion along with the completion of the Quatran project.
 * North Joseon found the system as proof that Sq. Isles was indeed a government project by the USA to destroy them, and relations worsened.
 * South Joseon, on the other hand, is pretty happy that their allies are stronger than ever before. Also, something feels familiar about these machines.
 * Snowzerland was not very pleased with the USA soldier's taunting, but handwaved the mechs as "nothing a couple of nukes can't handle".
 * add more!

Trivia

 * The USA is currently considering intense training for Ursa pilots so that they can finally do something about those pesky dinosaurs.
 * For reasons that are clearly far too difficult to comprehend, countries that own members of the Constellation System have a tendency to sometimes just kinda forget that they have them, even if they're, oh I don't know, fighting a giant cyclops robot or something along the lines of that.