Gaintoria No Hangeki

This is a tale about a floating continent . 6 years ago , a disastrous monster attack marked the beginning of mankind’s extinction . This is a story of the remaining survivors who struggle to fight and learn about these mysterious monsters as they prepare for a great counter attack . Will they succeed and regain their rightful rule of the continent? Or perish before these monsters.
Original manga is published on the artist’s pixiv page.