Kouya no Kotobuki Hikoutai Gaiden: Oozora no Harukaze Hikoutai
Japanese title: 荒野のコトブキ飛行隊 外伝 大空のハルカゼ飛行隊
Type: ONA
Episodes: 12
Source: Original
Genres: Action, Adventure
Studios: WAO World, GEMBA
Producers: Digital Frontier, Bandai Namco Entertainment, Bandai Spirits
Duration: 14 min per ep
Rating: PG-13 - Teens 13 or older

A short spin-off anime released on "Kouya no Kotobuki Hikoutai: Oozora no Takeoff Girls!" game app and YouTube.

(Source: AniDB)