Sky Wizards Academy (2015)

Humanity was driven off the land by the threat of magical armored insects and now live in aerial floating cities. Its defenses lie in wizards who fight the insects with magic in mid-air. Kanata Age is a young man who lives on the floating wizard academy city of "Misutogan." He was once celebrated as the "Black Master Swordsman," the elite ace of the S128 special team. However, he is now despised as the "traitor of the special team." One day, he is assigned as the instructor of E601, a team that has suffered 10 consecutive defeats. E601 has three girls — Misora Whitale, Lecty Eisenach, and Rico Flamel — with one or two peculiar quirks.

Source: TMDb