Sirius would recommend warping through his books, which is a good idea, but I couldn't execute it very well. So then I just stay behind him a little while before he starts firing the books, then walk away (towards the side he's facing) until the books start reaching me, then I double jump the other way and do an Ignis, and maybe a slide when I land, just in case the last book might hit me.
Something to that effect. I trust you know how to efficiently dodge the ice, Globus and lightning, yes yes?