One Piece: Unreal Adventure - Chapter 48: Let go!

An average man is reincarnated in the world of DxD! How do you survive in a world of battle-hungry monsters? With a cheat skill, of course! Devour the competition, becoming stronger with every fight! From the depths of the Familiar Forest, the Beast King will rise. (Harem, Gamer!SI)

This is a story about exploring technology in a wizarding world.Probability, electromagnetic induction, nuclear physics and theory of relativity—all of this can be mastered through scientific exploration and learning.Richard had always thought so… until he transmigrates to a world similar to the Middle Ages and becomes a prince. In this world of wizard and magic, he embarks on a journey to explain magic with science. One day, a dragon takes him away.“This is not in line with aerodynamics? It does not satisfy the Kutta condition, Circulation Theory of Lift and Bernoulli's principle either? How can it fly? Is there a special power source in its body?” Richard could not help saying as he glances down at the huge dragon he was riding on. “Well, I need to research this.”“By the way, you said you kidnapped me to find a playmate for your daughter. That doesn't sound like a good reason, right?”“Roar!” the dragon hollers furiously and waves its wings, soaring into the sky.Will Richard be able to continue on his journey of exploration and unravel the mystery of the wizarding world?

Once through the pirates, Lu En became the son of Monkey d Dragon, a grandfather named Monkey d Karp, and an unreliable and neurotic younger brother named Luffy.

Fortunately, the ghost back system is activated!

The completion of the ghost back is 10%, and the training effect is increased by 100 times!

The completion of the ghost back is 20%, and the training effect is increased by 1000 times!

…

One day, Lu En, a ghost-backed master, appeared in front of Luffy who was shouting to go to sea, and made Luffy cry on the spot.

Luffy: “The pirates in the sea are all monsters like my brother? I don’t want to go out to sea!”

Garp: “For a long time, the two boys, Long and Luffy, with small arms and calves, I really doubt that they are not my sons and grandsons. Like Lu En, they are the grandsons of the old man!”

Warring States: “The strongest creature in the sea, land and air is Kaido? No, it’s Lu En!”

- Description from novelbuddy

I have calculated for people before I was born, and I have all five yin, and I am born with fierce ghosts. A knowledgeable gentleman said that I will not live to be seven years old. After death, I will cultivate blood-clothed little ghosts to harm people.

In order to save me, my grandmother married me a child-in-law, so that I had an Ann birthday, although I later discovered that the daughter-in-law and sister-in-law are not human…

I have been lingering and panting since I was a child, and I have been accustomed to accepting it, but my grandmother was killed.

For this reason, regardless of karma, I inherited my grandmother’s job of raising ghosts and vowed to send everyone who killed her to hell.

- Description from MTL