Boukenou Beet

It's the Century of Darkness where monsters known as Vandels rule the world, and the Vandel Busters are the only ones who can fight them. When a group of Busters are killed in battle, they pass on their magic Saiga weapons to Beet, making him the strongest Buster ever. But Beet won't just fight the Vandels—he wants to destroy them and finally end the Century of Darkness. (Source: VIZ Media)