So the story is he killed the demon king, but got returned to the time when he was a child. He started training and building a reputation to become a hero. He digs behind a dungeon and just goes straight into the treasure room, so he could fund his career as a hero.

If I remember correctly, he also has a friend who is lazy but crazy strong. I remember in later chapters, they visit the demon country and contact the demon king, who is actually a demon queen. The friend has a sword that was used to slay the demon king before her. I remember that the new demon king is cloaked but has trademark black wings.

Note: not isekai manga. The protagonist just came back to the time when he's still young.


1 Answer 1


I think this might be Tsuyokute New Saga.

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Synopsis from MyAnimeList:

At long last, the demon invasion is over. The hero Kyle Lenard has struck down the Demon Lord with the aid of his companions and brought peace to the land. Although the fighting is finished, the land is in ruin. Most of the heroes have fallen one by one, leaving a mortally wounded Kyle as the only survivor.

With his strength fading, Kyle accidentally activates a mysterious artifact within the slain Lord's lair and is sent back in time to a few years before the conflict. Suddenly gifted with a second chance, Kyle reunites with his friends Seran the swordsman and martial artist Riize. The group must once again rally together a fighting force and use Kyle's knowledge of the future to prepare the world for a war no one else knows is coming.

Plot points that match your description:

  • The hero kills a Demon Lord at the beginning of the story, but is severely injured himself.
  • He sees a jewel in the Demon Lord's lair, and picks it up. Suddenly, he wakes up in bed, in the body of his younger self. This jewel is later revealed to be a dragon's heart.
  • The hero and his friends dig for and find a treasure room in a great labyrinth.
  • In later chapters, the hero and his friends meet the new Demon Lord, who turns out to be a woman.
  • The new Demon Lord wants the sword belonging to the hero's male friend, which she says was used to kill the previous demon lord, her father.

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