Lin En, a transmigrator with memories of his past life, finds himself reborn as the sole survivor of the exiled Valper demon clan in a world blending modern Japan with the supernatural underworld. Living quietly as a half-human, half-demon hybrid, his peaceful existence is shattered when Sona Sitri and Rias Gremory arrive to dissolve an ancient marriage contract. Lin En quickly exposes the political naivety of their request, revealing that publicizing his survival would invite deadly retaliation from the factions responsible for his family's massacre.

Forced to reconsider their approach, Sona begins to see Lin En not just as an obstacle, but as a complex individual worthy of respect. As Lin En navigates the dangerous politics of the Devil nobility while hiding his true potential, he begins laying the groundwork to build his own powerful peerage. With knowledge of future events and a pragmatic mindset, he turns a potential engagement crisis into an opportunity, all while secretly evaluating candidates like his classmate Aoyama for reincarnation.

In a world where power dictates survival, Lin En is determined to rise from nothing and forge a destiny that defies the expectations of both humans and devils.