Demon King X Hero

Essentially the demon realm  has been at war with the human world for approximately one hundred years, neither able to get the upper hand over the other. The Hero is a boy born with the potential to kill the Demon King and gain the humans a temporary advantage over the demons that which could possibly win them the war, but he has to make it there first. The story centers around Lillith - one of the Demon King's twin daughters - and the Hero as both travel through their lives. They won't meet much so we'd have to double up on characters. . .