Even if you were in the right, which you wouldn't be if you used any of Square-Enix's intellectual property (names, places, races, etc), Square-Enix could just pressure you with a lawsuit until you removed your book and possibly other legal consequences.
Even if you were in the right and Squeenix didn't like it, they could tie you up in a costly legal battle for however long it took to drain all of your money away and you couldn't fight back.