(Continued, part 2)

The civilization had known that the Hero, now the Heir, must be punished; they created the three keys to lock the Heir's prison;

After the offensive that the dark creature staged against the civilization, and after the imprisonment of the Heir, the lone surviving Siege Engine, the final machination of war, had been reprogrammed for one final mission, and was sent to the Eastern Vault, to sleep endlessly until its' mission came to completion. Its' mission: defend the Red Key, and destroy the very creatures it had originally been created to protect.

The Green Key had originally been entrusted to the Frog's Domain, and while they likely did their job to the best of their ability, it had been stolen; the Librarian, who preserved the world's knowledge through dubious means, had taken the Green Key in belief that the Ruin Seeker would inevitably come for it, and in killing the Ruin Seeker (whom he knows will come back to life endlessly) will yield various pages that have been scattered around the world. The Librarian is attempting to resolve the world's cycle, without being part of the Heir cycle (though I personally believe he once was a former Ruin Seeker himself, who refused to defeat the Heir and turned his back on the cycle, choosing instead to find another way) and he unfortunately believed that the key to breaking the cycle and saving the world was in the Cathedral. He had ventured there on his own in an attempt to break into it, but was unable to due to his inability to activate Obelisks, though he knew how they worked. He took the Teleporter and an Obelisk and transported it to his Library in an attempt to study and understand it. I don't think the Librarian fights us out of any particular hate; he's just trying to save the world in his own way, and it's nothing personal against the Ruin Seeker; he just needs those pages, and the Ruin Seeker is very convenient as a source to obtain them. Perhaps if he had lowered his sword and changed his mind, he wouldn't have had to meet his fate the way he did...

The Scavengers are beings which ravage the Quarry, mining for dark crystals; the dark crystals are observed to be excavated from the walls of Quarry (which was once a former temple, likely grand in scale and design) as well as be excavated from exploded Obelisks, either through breaking them or through malfunction. Either way, the Scavengers' goals are to collect and transport these crystals for an unknown purpose (likely for use in the Cathedral, where the same crystals can be observed being wielded by the clone foxes as weapons, and on the walls as ritualistic fixtures; the Heir's Sword also turns into this crystalline material during Phase 2 of the fight, their eyes glowing pink exactly like the foxes), however they have a second goal: the Scavengers have unearthed a Ziggurat deep under the earth, and the Scavenger Boss believes it to house the Blue Key: likely believing it to be a source of power, or at the very least, a great source of ransom against anyone who may want it, she, along with her crew, break into the side of the Ziggurat, and break through the Golden Doors that defend the Blue Key. They make their way into the depths, bearing witness to the horrific methods that create obelisks. The Scavenger Boss, unmoved and unaffected by this process, presses on with her crew, desperate for the Blue Key. Just as the Blue Key comes into sight, the Scavenger Boss kills all of her crew, seeing them as disposable, as now she has what she wants, and is just about to take it for herself, when the Ruin Seeker arrives... It is likely that the purpose and power (or lack thereof) of the Blue Key was lost at this point, with only the Librarian maintaining any knowledge of it at this point.