Kouya no Kotobuki Hikoutai Gaiden: Oozora no Harukaze Hikoutai

荒野のコトブキ飛行隊 外伝 大空のハルカゼ飛行隊

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