The Worldweaver's Sacrifice

You have already lost much of your money to ale and poor bets, so, lightheaded and light pocketed, you sit back and let the sound of music and stories told by strangers wash over you. They all wash together until one of those strangers starts becoming louder and increasingly more disruptive to your drunken meditation. You look up and see an older fellow hunched over a table with two unimpressed tavern patrons watching him scrawl on the table in charcoal and occasionally smack the drawings to emphasize his point. You consider yelling at him to shut his trap, but reconsider once you actually start to consider what he is saying. "The multiverse isn't so much a quilt or a series of planes stacked atop each other, as some have posited," the man said, somewhat exasperated, "but rather it more resembles the foam that rests on the top of your glass. See all those tiny bubbles sitting there?" He asked, pointing to the glass of ale one of the patrons was nursing. The patron nodded, rolling their eyes, and the man continued, "It's like that. All those bubbles are their own universes; some very similar to each other, some further away and very different. But, unlike the ale, whose bubbles stay the same size until they pop and make holes in the surface, the bubbles in the multiverse are sturdier and continue growing as forces of power within it expand. When one universe becomes too big, it pushes on the others, sometimes briefly losing or taking things from its neighbors. If this continues, it risks splitting and pouring into those universes, or having them enter into theirs. The gods knew how dangerous this could be if two or more dissimilar universes converged; how the gods and men would war until both were destroyed. So they created a tool to protect us if that ever happened. Some call it the Worldweaver's Sacrifice, others the Anchor of Erathis. It is unclear what exactly it does, but one thing is certain: in order to protect this universe, the Anchor requires that another universe is destroyed. I sincerely hope we never have to find out what other horrors it could bring or who has to bear the burden of being the one to destroy millions of lives to save their own." The man ends his story and the table is quiet for a few moments before the two patrons laugh and get up from the table, mocking the man as they walk to bring their ales somewhere less strange. When you look back at the man, you find he is making silent eye contact with you. With a curt nod, he acknowledges your interest and looks away, but his words still ring in your ears.

Summary

The Worldweaver's Sacrifice, also known as the Anchor of Erathis, is a tool created by Erathis, god of civilization, to be used as a last resort in the face of universal destruction. In the event that a universe is being encroached upon by one or more other universes, the Anchor has the ability to completely destroy one and allow the contesting universe(s) to fill the void it leaves behind. 
The Anchor resembles a sheathed dagger. The hilt, which protrudes from the sheath at an angle which suggests it is in the process of being removed, is made of cold obsidian and inlaid with streaks of platinum. The surface is polished with the blood of a god and reflects the face of its wielder with absolute clarity so as to remind them they they are personally responsible for the outcome of their endeavors. The sheath, conversely, is soft and comforting, made of thousands of thin multicoloured silk threads. Each strand represents a life which is to be taken when the Anchor is used. Though they are made of soft material, they are wound so tightly that there is no give to them, as if they were forged of steel.  
The Anchor was constructed so that it would take a source of power beyond that which could be produced by mortals to be unsheathed, but requires a mortal hand to be turned against another. Once unsheathed and held, it requires a final sacrifice to ensure that the weapon is being used for the benefit of many and not just its wielder: the weapon must be used on a person from the universe they seek to destroy, and that person must trust or love their attacker.

Historical Basis

Many centuries ago, some the gods began noticing their followers receiving what they believed to be divine gifts coming from other gods. They fought amongst each other, each concluding that their power and influence was being tested so that they might be weakened and overthrown. There were many years of conflict until Erathis, Pelor, and Asmodeus shared what they knew and concluded that the influence was coming from outside of their own universe. Terrified by the implications, they each set about creating safeguards against a full incursion by whatever force was responsible. Pelor and Asmodeus worked to strengthen the barriers between the different planes of existence within the universe, paying special attention to the Feywild and Shadowfell, which they concluded were the easiest ways to enter the material plane. Erathis then began the process of creating a weapon which could be used if the situation became more dire and they were left with no other choice. This eventually became known as the Worldweaver's Sacrifice and was kept by her followers in rotation so that it could never be used to unnecessarily destroy another world. It changed hands so frequently that it was eventually lost to time and myth. At present, nobody is entirely sure where it is being kept.

Spread

The myth was only ever known to a very select few, most of whom have since died. Now, the story is rarely spoken of and has been denounced as fiction. Who would believe a story where Erathis, Pelor, and Asmodeus worked together for a common cause? What kind of message could that be trying to convey? Worshipers of all three would rather give their lives than admit that their chosen god could have worked with a being so opposed to their views. Still, scholars who study the multiverse and take the time to seriously read through the scattered texts which reference the Anchor believe that there is a chance that it might exist.

In Art

Though many of these images have been lost or destroyed, there still exist in temples and shrines paintings and statues of Erathis hiding a dagger behind her back though there are no enemies or other motifs of war in the piece. Some claim that she seems distracted in these pieces, but nobody can agree if this is true or what she could be concerned about.