House Xianthelipse was a minor House which would have rose to prominence during the War.
Just prior to the outbreak of the War, the Homeworld's War King encouraged the Houses to consider how they might adapt. Xianthellipse took this to extremes, experimenting with new forms and biodiversity. (PROSE: The Book of the War) They developed 'war forms' for the Great Houses that left them indistinguishable from monsters. (PROSE: In the Year of the Cat)
Nevertheless, Xianthellipse took its place with those two among the six ruling Houses, along with Tracolix, Dvora, and Lineacrux, filling the gap in the social hierarchy that had previously been filled by previous Ruling Houses. (PROSE: The Book of the War)