Undercover in the Demon King's Castle, My Goal Is to Save the Princess Knight!

After accidentally transmigrating, Loka became a hero alongside five beautiful girls. He thought he was about to reach the peak of his life, but...

Why was his perspective after reincarnation so strange? He had actually been reborn in the Demon King's castle as the heir to the head of a succubus family?!

And that wasn't all. Why had his fiancée, the young vampire princess, ascended to the throne of the Demon King???

He heard that the other five heroes were struggling to make headway. Meanwhile, in the Demon King's palace, the young man, now head of the succubus family and one of the most influential demons in the entire castle, stroked the Demon King as she slept peacefully in his arms.

"I'll be the one to save humanity's future!"