Maou no Migiude ni Natta node Gensaku Kaiakushimasu

Tohru, a passionate fan of the "absolute evil" Demon King, who died as the symbol of the happy ending of the manga ‘Lapis Lazuli World', was in despair. "I wanted to dedicate everything to you." Such was Tohru's last thought as she fell from a high building. The next time she woke up, she had already transferred to the Lapis Lazuli World. And to the castle of her beloved Demon King, at that! (Source: Novel Updates)