The Belfry Guards are marionettes created by the Princess of Venn and the Prince of Alken to protect their respective bells. The twin bells symbolize the bond between two lovers who could never be united. The bell keepers are their eternal guardians. To this day the forbidden love of the Prince of Alken and the Princess of Venn manipulates these marionettes, a feat that has outlasted their own kingdoms. They will stand watch, forever and ever – these determined, if ill-fated, marionettes.
The Belfry Guards are the leaders of the Bell Keepers covenant and recruit Undead to protect the bells. They are the faithful guardians of the bells, ever ready to annihilate trespassers. Their primary purpose seems to be to ring the bell themselves (“Gather around, and ring the bell swift! We’ve been ringing this bell forever, we have! Ah hah hah hah!”), and to make sure that those outside of the covenant do not try to stop the bell from ringing (“Keep your hands off our bell!”, ”Stay away foul Undead, or you’ll be a goner! Hah hah hah hah!”, “When you’re round the bell you’ll be brought near! When the bell is in trouble, the ring brings you here!”). The protection of the bells is for the Prince and Princess’ honor.
From this we can take it to mean that the Prince and Princess gave these bells to each other, so that when they were able to hear them ring, they would be reminded of their love. The Belfry Guards were designed to ring these bells and maintain this situation. There would be some, most probably within the kingdoms of Alken and Venn who understood the true purpose of these bells and sought to bring an end to it. To counteract this, the Belfry Guards were instructed to slice to bits any who might approach the bell.