Rumia and Sisti are mages-in-training at a prestigious magical academy where they hope to be taught by the best of the best. However, when their favorite instructor suddenly retires, his replacement turns out to be a total jerk–he's idle, incompetent, and always late! Can Rumia help uncover their new teacher's true potential—and can Sisti still learn magic and unravel the secrets of the mysterious Sky Castle with such a terrible mentor as her guide?