The first two in a series of non-existant techno-magical-medieval books. Both covers are built from the same layers, the differences were created by re-ordering the layers, and changing the layer blend modes (with some extra level adjustments and tweaks, of course, but you get the idea...)
Of course, I have to acknowledge that the first book's title probably owes something to a comic book that Epic put out back in the 80s called "The Sisterhood of Steel."
And the title of the second book is a (mis-heard) lyric fragment from the song Daredevil by The Tragically Hip