CEO's Secret Lover - Chapter 815

As the heir apparent of the Ye family, Ye Xuan went through fire and water for his family, but Ye Lang, who had just awakened his Divine Soul, usurped his place. In order to keep his position, Ye Xuan challenged Ye Lang to a Life-death Duel. With the broken Dantian, would he win this fight? The black ring his mother left brought him a great opportunity: Realm Hell Tower, where he met a mysterious lady, who told him to look for nine Daoist Laws to enhance his strength and gave him the Spirit Heaven Sword. Could Ye Xuan find all the Daoist Laws and become a powerful swordsman?

- Description from Novelupdates

Reborn into the world of Yugioh, it's natural if my goal is to become the best duelist!

“Mr. Xu, are you really a Heavenly Master?”

“As genuine as they come, more real than gold!”

“I’ve heard that your reputation in the supernatural circle is really bad, even to the point where a ghost once called the police saying you were threatening him?”

“Impossible!”

“It wasn’t me!”

“Don’t talk nonsense!”

Xu Yang clenched the Thousand-Year Peachwood Sword in his hand, and said, “What’s the name of that ghost? Would you dare to let him confront me face to face?”

(PS: This book is also known as ‘This Heavenly Master is too Vicious’, ‘Scaring Ghosts Makes You Stronger’.)

This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.

Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.

“Please save us, Savior Dono!”

Kuroki nodded, deciding to save the demon king due to an unexpected turn of event.