Tirving in both hilt and soul forms
Tyrfing (티르빙) is Elmar Hyacinth's Supporter. In an uncontracted form, she looks like a non-bladed hilt, but once a user tries to contract with it, they are sent into Tyrfing. There they meet its soul form, that of a pale, nude woman in a pool of blood. The supporter itself grants the user with more power, the more blood it's given. The blade of the weapon itself is a blade made of blood, and should the user not give Tyrfing blood daily by killing his or her enemies, it will draw its own user's blood via two small tubes connected to the master's arm via the hilt.
Because of this, Elmar, who has phenomenal healing powers and can stand to lose such large quantities of blood frequently, was the ideal, if not only, choice to become Tyrfing's master. Tyrfing refers to her master as "Foolish One" yet shows itself to be genuinely cooperative with her so long as it can be fed.