Ryuga Kiyotaka is an ordinary boy that you can find anywhere. But he has a big secret that he hides from anyone. Ryuga works as Professional Hitman or Assassin. He doing that to continue Kiyotaka's Family tradition and to repay their kindness.He is an Orphan, but he has a lot of talents to make him recruited as an Assassin. He never failed to do his mission and have a 100% success ratio.On a certain day, he was teleported into a Parallel World after he finished his mission by a wicked Goddess to become Demon Lord!!This is story about the adventure of the Strongest Hitman with powerful gadgets to find a way to return on Earth.