Brigadoon: Marin & Melan(2000)

Brigadoon: Marin & Melan is a sci-fi anime series that begins when a mysterious planet suddenly materializes in Earth's sky. Marin finds herself under attack from hostile mecha known as Monomakia, forcing her to seek refuge in an abandoned shrine. There she discovers an ampoule containing Melan, a sleek blue mecha with a fierce protective streak. Bound by an oath to defend her, Melan becomes Marin's unlikely ally as she navigates the chaos unleashed by Brigadoon's arrival. Together they must survive encounters with dangerous mechanical foes while uncovering the truth behind the planet's sudden appearance and its connection to Marin's fate.