Academy Blues is part of Daishi Prime's Deva series, set in the universe of Magical Girl Lyrical Nanoha. Because it was begin before MGLN StrikerS, the series is a divergence. Academy Blues is the second story in the series, follwing Path of Vengeance and preceding Endless Waltz.
The core concept of Academy Blues is that having served the TSAB for a decade, Hayate returns home to Earth and founds an academy to recruit and train Earth's potential mages in using magic. Her first class of sixteen teenagers are recruited from all around the globe and are handpicked for intelligence and magical power.
Almost immediately, the Academy comes under investigation and later attack by the Circles, a global organisation of Earth's existing but well-hidden hermetic magical traditions who see the use of Devices as heretical and potentially destructive to the entire planet. The conflict escalates steadily to open battle, disclosing magic to the public.