[Traditional light novel style + otherworld + school + pseudo-harem + sister complex + battles + Demon King and Hero + Cthulhu] If one day you gained the Demon King’s power and became the Demon King yourself, would you, like the protagonist of this book, Sakata Sei, use it only to protect the one sister you love more than anyone? Or would you destroy the world and rule supreme, like a true Demon King?
