The Blood Blades were created thousands of years ago by immoral and reprehensible means by a cult of hereitcal Humans. Their cult believed that blood was the essence of the Soul, and could bring them great power. They conducted blood rituals and sacrifices in order to forge the blades. The blades all utilize the blood of the user in their function, their blades being enhanced by an edge of blood.
The process of creating a Blood Blade involved heretical rituals and sacrifices, often costing multiple lives just to create a single Blood Blade. The process is also unstable and unpredictable, with no two Blood Blades being the exact same, and many simply breaking under the power being instilled within them or failing to become Blood Blades outright.
The first successful Blood Blade created was Bloodrend, and all the others would copy its design, though none would surpass its power. As the first Blood Blade, it was also the only one to recieve a proper name, though it received the name Bloodrend later on, as its original name was lost to time after the cult that had created it was destroyed.
It is unknown exactly how many Blood Blades were created or how many still exist.