Memory records of bastard magic instructor

Sisti is a magic-user in training who attends a prestigious magical academy where she hopes to be trained by the best of the best. However, when her instructor suddenly retires, his replacement is anything but what Sisti had hoped for—idle, incompetent, and always late! Can Sisti still learn magic and unravel the secrets of the mysterious Sky Castle with such a terrible teacher as her guide? (Source: Seven Seas Entertainment)