Past Life & Reincarnation: The main character, Kiyoshi Ishida, is reincarnated into a new world after his death.
The World's State: The new world is infiltrated by demon lords, and history regards a "hero" summoned 100 years prior as a savior. However, this hero is a secret villain who now manipulates humans using the demons for his own ends, creating a false peace.
New Beginning & Powers: Reborn as a mysterious child to veteran adventurers, the main character is trained in magic and martial arts. He discovers he can use ancient, forbidden time magic and understands a power that even the gods cannot control.
The Path of the Darkness Lord: Eventually taking the name Shujin (meaning "Master/Ruler"), the protagonist chooses to become the new Darkness Lord. Unlike the previous "hero" who acted as a puppet master, Shujin aims to establish a true justice, even if he must become a cruel and fearsome figure to do so.