Millimos Saga - Battei Ouji no Tensei Senki

After encountering a train accident, he is reincarnated into another world, where he is the youngest prince of a weak country in the mountains!? He was supposed to be enjoying a leisurely, slow life, but he mastered magic and sacred techniques on his own and became a military marshal. Milimos gains two powers that cannot coexist, and gradually becomes embroiled in a national war regardless of his will.