Saijaku Maou no Shinimodori Saiseitan

The manga centers on Krom, the second Demon Lord who is weaker than even the Seven Demonic Generals who support the Demon Lord. In the midst of his reign, the Demons' mortal enemy, the Seven Heroes, invade the Demon territory and slaughter all, including the Generals and Krom's devoted servant Shia. In his deep shame, he commits suicide to join his companions in death. But he then awakens to a time one year before his death. Now wielding his own death as his greatest weapon, he prepares for the calamity that awaits him in one year's time.

(Source: Anime News Network)