Harem Investment System: Getting Money And Women - Chapter 147: Caroline

In a world fractured by conflict and haunted by shadows of the past, Kokushibo—the first Upper Moon demon—meets his end, only to awaken in a new life. Reincarnated as Crimson, a child born into a different family, he carries the memories of a past he cannot escape. Burdened by centuries of guilt yet indifferent to the present, he resigns himself to duty—until an unexpected bond with his newfound family begins to thaw his hardened heart. As he struggles between the weight of his past and the weight of the new life, Crimson must decide whether he will remain shackled to his former sins or embrace the possibility of peace.

The world that nurtured the civilization which reached the pinnacle of magic was on the verge of destruction.
The last survivor transmigrated to the past, when the magic civilization started growing, as countless mages were still fumbling their ways through the thorny paths of magic knowledge.
He, who came from the end of the magic era, aim to reach the pinnacle of magic.

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Shaymon, the man who has achieved the apex of dark magic, is framed as being a Demon King and is killed.

Because my father was an Earl and my deceased mother had been a commoner, I was burdened with a narrow life as an illegitimate child. As a 16 year adult, I have decided to leave the aristocrat family registry and become a common citizen. I wonder if the knowledge I obtained as a member of nobility will help me in living as a commoner.