One Piece - I Am A Different Luffy! - Chapter 421 - 420 - Return to Skypiea.

“Missus, time to fulfil your duties!” Mu Yuchen demanded as he pulled Xi Xiaye closer with his arms intimately wrapped around her waist.

It was a meticulously planned feast for the powerful. Her fiancé had knelt down on one knee and proposed to her sister instead. Robbed of her right to her inheritance, she was prepared for the Xi family to throw her to the wolves.
As she slipped away from her family that had turned their backs on her, she found him — Mu Yuchen, the low-profile and reserved noble that ruled City Z and led Glory World Corporation.

“Mu Yuchen, let’s get married!” He looked up at her, then suddenly stood up.

“Where are you going?”

“Let’s go. Any later and the civil affairs bureau will be closed.”

- Description from Novelupdates

Kakashi has lived a sheltered life within the protective confines of a barrier, which shielded them from the dangers that lurk outside. Raised by his devoted mother, Ako, and loving sister, Tokah, he only know a world of happiness and joy. Living in a world where he thought nothing could go wrong.But when a group of men invades their home, everything changes. In the brutal assault, Kakashi witnesses his mother's tragic death, a moment that shatters his naive understanding of safety. While his sister manages to escape, Kakashi is captured and subjected to experiments designed to exploit his hidden powers.Years later, amidst the ruins of a collapsing facility, granting Kakashi a chance at freedom. Rescued by an academy dedicated to training gifted individuals, he discovers not only the extent of his abilities but also the resolve to seek vengeance against those who tore his family apart.Driven by the desire to reunite with Tokah and avenge his mother's murder, Kakashi embarks on a journey filled with action and self-discovery.As he navigates the treacherous underbelly of a world rife with superhuman conflicts, he must confront his own problems while mastering the very powers that once made him a target.

This is a world where humans, demons and mysterious beasts coexist. Humans cultivate mysterious qi. Demons cultivate corporeal bodies. Mysterious beasts cultivate soul perception. A legend says that in the middle of an endless rainforest, there are extremely powerful existences; they are called demon kings. Some demon kings have a tyrannical corporeal body, some are experts in illusions. Some demon kings are proficient in magic, some can even move mountains. Some demon kings are able to sense things thousands of miles away. These demon kings rarely appear in the human world. Even if they emerge in the human world, they would reincarnate in human form; assimilating with mankind while seeking to breakthrough realms…….

There was a mysterious old man who approached the failed swordsman with the “100 million years button”. A magic button which can achieve the same effect as training for 100 million years if you push it.

The failed swordsman who pushed the button had his doubts, but immediately felt tremendous power rising in his body. So he pushed the button many times.

However it was a cursed button. The moment it was pushed, he was confined to the 100 million years prison of time. The first 100 years were devoted solely to training. After 1000 years he had forgotten why he swung his sword. He stopped thinking completely after 10,000 years had passed. After 100 million years he became crippled and finally managed to return to the real world. At the same time losing all his memories from the past 100 million years, the only thing that remained were his sword techniques. “I can become stronger just by pressing the button!” or so he thought and pushed the button many times after that. Foolishly trapping himself in that 100 million years of hell each time.

As he continued this loop, he began to think “If I destroy this world, will I get out of here?” A few billion years later, he finally escaped from the loop.

This is the story of a failed swordsman trying to make a name for himself in the world.