For a Baskerville, Chains are not mere weapons.. but comrades in arms, with whom we exchange blood as equals, and equally share our destinies.
"Chain" is a term given to those who reside in the Abyss. A Chain is created when something drops into the Abyss, and though anything dropped into the Abyss can become a Chain, the process of becoming a Chain differs between beings without a defined consciousness and those who do. For objects that end up in the Abyss and originally lack consciousness, the power of the Abyss provides said object a consciousness and allows them to think and feel as all beings do when they become Chains. However, for those who enter the Abyss with an already defined consciousness will absorb the power of the Abyss to the point of saturation, resulting in the mutation of their human bodies and transforming them into a monstrous and misshapen being. Fortunately, after the transformation is complete the Chain can retain the personality it had as a human if its will is strong enough, albeit slightly altered by the Chain's new found voracious hunger and lust for power. In both cases however, the being is not considered by the Abyss to be a part of The Rule of 100 Cycles. As such, when a Chain dies, its life will fade from existence and disappear all together, since they're not welcomed to be reborn after 100 cycles.
Chains themselves lack the power to leave the Abyss of their own volition. Instead, Chains must either form a Contract using through one of the Doors to the Abyss or wait until there's a disruption in The Way that they can apply pressure to in order to rip a partial entryway into the 1st Dimension. Unfortunately however, a Chain's existence is unstable, and as such a Chain can't exist in the 1st Dimension without a Contractor to stabilize its existence. For this reason, when a Chain does manage to break through The Way and into the 1st Dimension they spend the minimal amount of time they have seeking out a Contractor and causing mass destruction by devouring humans in order to fuel their power. The only exceptions to this are The Black Winged Chains: Raven, Owl, Dodo, Gryphon and Jabberwock - who are able to traverse the various dimensions freely using their immense power.
Chains form Contracts through the exchange of blood between a Contractor and its Chain, however doing so without being a member of the Baskerville Clan, who are chosen to act as messengers of the Abyss by The Core herself, receive an Incuse with a time limit that allows the Contractor only twelve uses of their Chain's power. With each rotation of the Incuse, an "Illegal Contractor" will feel immense pain as a burden of the Chain's power. Although, the closer the Incuse gets to the 12th rotation, the more primal and Chain-like the Contractor becomes; acting more so like a puppet for their Chain to guide. As of the 12th rotation, the Contractor and the Chain are plunged into the depths of the Abyss, where the Contractor will eventually mutate into a Chain themselves. Carceres are the only known loophole to this state of order, as a Carcere will take in the Chain's blood instead, resulting in a Baskerville Incuse to appear on the Carcere. Though the Carcere is truthfully the safer method of forming a Contract, the amount of the Chain's power that's available for use is greatly lessened.