Kyoushu Ichizoku no Suemusuko wa Godai Maou no Chikara o Yado Shite Kaikii suru

The Valgred family is a notorious clan of skilled assassins, feared by all for their deadly prowess on the battlefield. Born as the youngest son, Glenn is deemed unsuitable for training due to his frail health, earning him the scorn of his father and his subsequent exile to a desolate wasteland. Left to perish amidst the harsh environment, Glenn is unexpectedly saved by Emperor Wilfoen Thorngrave, who takes him under his wing. To repay the debt of his life, Glenn dedicates himself unwaveringly to the empire, eventually playing a pivotal role in the defeat of the "Five Great Demon Kings" and emerging as the hero who brings an end to the Demon War. Nevertheless, his loyalty is brutally repaid with treachery by the very emperor he trusted, and Glenn meets a tragic demise at the hands of nine mysterious assassins. However, Glenn's story takes an extraordinary turn when he awakens to find himself inexplicably transported back in time to his youth, thirty years prior to his tragic end. Armed with the combat skills and knowledge he forged in his initial life, Glenn discovers that he now possesses the "Power of the Five Great Demon Kings," an extraordinary ability that grants him unparalleled strength and prowess. As he begins to reawaken, Glenn finds himself rapidly gaining power at an unprecedented rate, setting the stage for a new and potentially catastrophic chapter in his life.