The Origin Dagger has a wide blade with demonic runes carved on it as well as horns separating the blade from the handle.
The dagger was once hidden in a catacomb with its location buried inside Harry Greenwood's mind. Fiona Callahan later captured Harry in an attempt to get the dagger, so she could use it to destroy magic.
The dagger currently has been placed inside of Macy after she telekinetically removed it from within Parker. With this, Macy merges with the Source.