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An orphan girl Ren encountered an accident on the way to being sold, and the shock brought back her memories of her previous life! "I was an old man!!!" Yes, Ren's previous life was a researcher in his 30s who died in an accident, reincarnated as an orphan girl, and lived until now !! In order to escape from the merchants, he uses his hidden magical talent and scientific knowledge from his previous life to survive alone in a harsh different world.
During the school trip Touka and his classmates are summoned to another world. However, Touka was the only one with the lowest rank: E-rank an extremely low status compared to his classmates. Thus, the former mob-character and abandoned hero, will absolutely become the strongest devil as he advances and strikes back.