The Eminence in Shadow, Vol. 5 (light novel) — Daisuke Aizawa

All is well at the Midgar Academy for Dark Knights, but then something wicked suddenly draws near: The students are vanishing one by one -- even Cid's older sister Claire! Zeta of the Seven Shadows sets off to investigate while Cid and Alexia embark for Claire's room where they find...ancient scripts, a cool magic circle, and spells that seem like they have great meaning and yet absolutely no meaning whatsoever?!