The Yandere villainess loves the useless engineer

In a world ruled by magic and noble bloodlines, Leon Aldric wants nothing more than a quiet life away from the chaos of the future he remembers. But as tensions rise between kingdoms and wars as well as other disasters slowly approach, Leon begins secretly developing technologies far beyond the world’s understanding deep within the forests of his territories. At the same time, one girl continues to stay by his side— Lilith NightBane, the terrifying prodigy feared by nobles across the kingdom and the future Void Witch herself. While Leon tries to change fate from the shadows, Lilith seems far more interested in one thing alone. Him. — Description from novelcodex.org