Upon Fragarach's blade is a runic inscription of an enchantment said to have been placed there by Jak'ra himself. The enchantment states, "In the Hands of the King, I shall be free." In order for one to be "worthy" that may be up to the DM. However, most wielders of Fragarach have been willing to uphold a greater good for unselfish reasons, been dedicated to justice and truth, been willing to sacrifice their own happiness to uphold it, and been willing to protect the weak and needy regardless of their race, creed or culture even at the cost of their own life. If someone who is unworthy but not Evil attempts to lift the sword, they will feel as though they are attempting to lift an impossible weight and the sword will not budge. If someone who is Evil attempts to lift the sword, they will take 2d8 Radiant damage and be knocked back 25 feet.
Upon being drawn from the anvil, Fragarach is attuned to the person who drew it until their death or the DM no longer deems them "worthy".