Assassins vs Knights

A Japanese assassin, The Strongest warrior of the Unified Irish kingdom - Satoshi Kamado, was assigned to train the cadets from the military instituition Dullahan, as monsters' attacks get more violent, coordinated and deadly each year. The humanity needs a hope, and his ellite squad must become that hope. The only difficulty is that his comrades keep dying. His step-sister and his lover - assissin Kali Carsvell - is the only person in the world, who willingly protects him, when everyone rely on his protection. Dullahan is an Irish monster that is called a headless rider on a black horse, who carries his own head. The students of this instituition are self-sacrificial warriors, classified into knights and assassins, who are destined to die for humanity. Satoshi and Kali are not the only ones, who refuse to lose their loved ones.