Miss Savage Fang, Vol. 1 (manga) — Kakkaku Akashi

Envil, known by the title “Savage Fang”, was a renowned mercenary who should have died fighting in the civil war. Instead, he awoke back in time -- inside the body of the very tyrant who started the war in the first place! Mylene Eltania was the world's most beautiful, most ruthless empress. With beautiful hair signaling her divine gift, and beauty beyond compare, she was a force to be reckoned with. Now, this mercenary has a second chance to fight back before it's too late. Mylene's beauty on the surface, but a savage beast rages below!