Rule the World, Starting from Merging with the Demon King

"Have you ever heard of the legend about a brave man who killed the devil three hundred years ago?" "Of course I've heard of it. Who in this continent hasn't heard of it?" "I have here the autograph of the leader of the brave team." "Who are you kidding? I still have the second-hand armor worn by the leader." Yueying, who was counting the money behind her, spread her hands helplessly and realized that the ones she had worn were not counted. ... The female students of Star Dome Academy screamed and cheered. "Ahhh, Kaikage-sama is so handsome. You should find a partner like Kaikage-sama." The male student exclaimed in amazement. "No, buddy, your hands-on super-level magic is too exaggerated." "No, why did you use this ancient sword technique to kill seven familiars? Are you not a magician?" In response, the two souls in Kaiying's body just laughed. "Because standing in front of you now is Keitel, the empire's number one swordsman from three hundred years ago, leader of the brave team, and the world's strongest Demon King Yueying, who has caused harm to the world for thousands of years!"