The Ritual Dagger is a very important item in the rituals of the Necromancers of Pagan, used to send people to Lithos. Due to the precise nature of their rituals, only this one dagger will avoid the anger of Lithos.
The Necromancers had used the dagger many years, until days before the Avatar arrived, Mordea came with guards and forced Vividos to give it up, so that rituals could only be done with her permission. Vividos was upset with the situation, so when he met the Avatar in Ultima VIII, he requested the hero find a way to return the dagger. Talking to Aramina, the Avatar received the key to Mordea's private storage, and retrieved the dagger. The Avatar returned it to Vividos just in time to send Lothian to Lithos. Impressed, Vividos offered the Avatar the opportunity to become his apprentice.