-----Original Idea-----

It all revolves around this alternate plane of existence, parallel but completely separate from the real world. It's called the Broken Realm... And sometimes, people from the real world find their way into it, either through an artifact of some sort, or perhaps a freak accident of nature, or sometimes even being led there unaware by someone who is capable of shifting between the Broken Realm and reality, either by their own will or by use of such an artifact.

And the realm is... Well, mostly broken. The landscape is shattered and destroyed, leaving empty space in between infinite voids of nothingness. Sometimes theres a sky, sometimes theres not, depending on what 'sector' of the realm you're in. 

Sentient beings who find their way into the Broken realm eventually find their way to the Citadel, where other sentient creatures have gathered in a large metropolis. The members of the Citadel have learned to form bonds with one of the Broken Realm's native creatures, which they call Guardians, and which take the form of a spirit that resides in a specially attuned piece of wearable whatever -- gloves, hats, jewelry, whatever. 

Guardians are able to capture, store, and manipulate Aether, a powerful force that is found all over the broken realm. There are different colors of Aether, which all have different effects, and guardians come in two flavors too.

Some guardians have the power to restore, heal, protect, and most importantly, to reconstruct the broken realm, through the use of Aether. The sentient creatures who choose to bond with these guardians are called Menders.

Some guardians have the power to hurt, attack, and even destroy the broken realm. The sentient creatures who choose to bond with these guardians are called Breakers.

But they're not enemies with one another. These Breakers and Menders rally at the citadel, where the leaders of the citadel guide and direct their actions in order to restore the broken realm, to protect it from the encroaching evil that destroyed the Broken Realm to begin with... Some of them stick around to protect said realm, while others are just looking for a way to get back home. Whatever the case, the citadel provides a safe haven for them.

Menders and Breakers work in pairs of one mender, and one breaker -- another bond which the Citadel assists in setting up, although it is not quite as permanent as the bond with a guardian. They work in pairs because while Mender can move almost freely through the Broken Realm, due to the evil presence they are sitting ducks, because their guardians are very limited in offense. Breakers on the other hand are naturals at destroying pretty much anything, but their ability to mend the landscape  and actually travel about is limited, and  due to their close encounters with bad things they tend to get dinged up often -- something that Menders could heal, or even outright prevent.

The ideas in my head at work played out almost like a video game. teams of two would scour the broken realm, some of them looking for aether to fuel their guardians, others looking for actual physical treasures, many of which had unusual properties. Some were just looking to explore new reaches of the broken realms, mapping out never before visited places using high-tech wristband thingies similar to pipboys, that most people kept with them as maps or communicators. Still others were in it for the thrill of the hunt, seeking out increasingly stronger enemies to destroy... Some of them were doing it to protect the broken realm, some of them to protect the citadel, some of them were just looking for a way home...

------Addendum 1-------

Okay. I've decided that guardians aren't sentient things that inhabit inanimate objects. Guardians now, almost invariably, take the forms of small quadrupedal creatures, and im visualizing them to look very similar, but not quite, like Eevee and its evolutions, with a few unique ones here and there such as snakelike guardians, birds of prey, etc. They're totally sentient and talkative. The idea of an inanimate object that can only speak to the mind of the one it's bonded with seemed boring.

People don't just accidentally get into the broken realm. Guardians pick out individuals from the mortal realm that they feel are capable or worthy of being brought to the broken realm. Typically they pick out individuals who are extremely down on their luck, with little to nothing left to lose, because....

Being taken to the broken realm is now a one way trip. there is no going back. Originally i thought of methods that would let individuals return, but decided against it. Due to this, Guardians typically throw out a lot of warnings when bringing people there, as they cant be brought back.

They do this because guardians exist on a third plane of existence called the aetherial plane. They were locked out of the broken realm when said realm was... well, broken -- By a guardian who seeks to destroy everything, starting with the broken realm. (Previously, it was some ambiguous evil). Mortals are not locked out of the broken realm due to their mundane nature, so in order to bypass things, guardians bring mortals to the broken realm and bind to their souls, giving the guardians the chance to fix things, and in return, lending amazing powers to the mortals.

Menders and breakers arose because some guardians excel at destroying things (Red, yellow), some so much that they cannot do anything BUT destroy (Black).... while other excel at protecting or creating things (blue, green), some even to the point of being incapable of doing anything BUT that (White)... So it made sense to pair menders and breakers together, as they generally complement one another.


-----Addendum 2------
The Mender/Breaker duality has changed. Both menders and breakers can restore broken parts of the realm. However, the same guardians that were menders (Blue, Green, white) still excel at it moreso than the others. Black still cannot mend.

Mending is, for the most part, a temporary process. Only creator-tier white guardians can make it permanent, through use of white creator powers.

Speaking of which, there are two types of white and black guardians now; the standard guardians and the creators. Creators are extremely uncommon and powerful. Elder creators create and maintain entire universes -- younger creators beneath them assist them in maintenance until they've learned enough to venture away from the universe and start their own.

The Mender/Breaker titles are still used, and refer to what kind of role those individuals play in combat. Menders tend to be more on the supportive and defensive side, while Breakers tend to be more offensive. However, Breakers DO have defensive capabilities, and Menders have offensive abilities. Black and White are no longer purely offensive and defensive respectively; They simply lean very heavily towards it now.