Tensei Shitara Isekai Saikyou no Kishi Danchou

When Fujimura Yuuji is hit by a truck and meets his untimely demise, he finds himself reincarnated in a fantasy world, in which he's the commander of the Knights of the Holy Order, destined to save the land from its destruction at the hands of fiendish monsters. But his mission goes awry when his fiendish foe proves too powerful, and has its way with the hapless paladin.