Prelude to Dune? establishes that immediately prior to the events in Dune, House Moritani are at war with House Ecaz. In the year 10,175 A.G., the Viscount Hundro Moritani allies with House Harkonnen in an attempt to conquer the Atreides homeworld of Caladan; the attempt fails when the Atreides Mentat Thufir Hawat tricks the Moritani/Harkonnen forces into believing that the Atreides have a gigantic water fleet, which are actually harmless fishing boats. House Moritani also attacks the planet Ginaz after some of their students are sent home in disgrace from their renowned Swordmaster School.
Paul of Dune? reveals that House Moritani is secretly descended from House Tantor, the renegade house who had devastated Salusa Secundus with atomics and who had been subsequently "exterminated" by Padishah Emperor Hassik Corrino III. Their name disappears from written history. It had been established in the Legends of Dune? trilogy that prior to the Butlerian Jihad, the Tantor family had adopted an orphaned Xavier Harkonnen.