Eheheheh... Their souls, and their bones. It's mostly decorative, but I feel it helps keep the souls under my absolute control to have a part of their bodies contributing to the design of the guard and handle. The blade itself was made by taking simple infernal iron and melting it together with the charred bones of my conquered victims until it made a high grade steel. The steel was then melted again, and combined with a sample of my own flesh.

That last part is critical if your master wishes for a weapon that is truly his and his alone. You must add a part of yourself to the very metal of the weapon, thus making the weapon a part of yourself. A hand, an arm, a leg... I went with my heart quite literally in this regard. Your Lord Andras should not fret about this. Whatever he gives to make the blade his, it will grow back.

While the steel was forged into blades, binding runes were carved into their surface. This is why the introduction of a part of yourself is an important step. This binding process enchants, and curses, the blade, ensuring none other than yourself can wield it, and it cannot be used against you. I can even see and feel through the blades. I can control them, to a degree, without touching them. I can channel my power through them. They are my weapons, and my weapons alone.