Shin Kaku Gi Kou to 11 no Hakaimono

A powerful evil god exists in a world where swords and magic are common. People both fear and desire the god's immense power, which leads them to break off its horn and forge it into ten powerful magical weapons known as Shin Kaku Gi Kou. Each weapon is strong enough to defeat a nation and its military. Moebius, the most skilled wielder of these weapons, passes his power to a boy named Miyabi before dying. He warns Miyabi about the threat of an unknown eleventh user and the danger of a monstrous force that could destroy the continent.