REGALIA: THE THREE SACRED STARS

Twelve years ago, a mysterious event shook the Kingdom of Rimgarde, causing massive destruction. In the present day, Empress Yui rules a peaceful kingdom where she is loved by her people and especially by her sister, Rena. But when a giant robot appears, her peaceful life is shattered. Now Yui must fight to protect her nation and the person she loves most. (Source: Funimation) — Description from AniList community (anilist.co).