ダーリン・イン・ザ・フランキスXX Darling in the Franxx

From the introduction:

Far in Earth’s prehistoric history, millions of years before human civilization rose to prominence, Earth was inhabited by a species known as Klaxo sapiens. They were a humanoid race with horns and blue skin, and possessed a technology base much more advanced than that of humanity. They were a peaceful species though, and they lived in harmony with nature as they advanced their society, but their whole world was thrown into disarray when they were invaded by an alien race.