Transmigrated as the Tortured Female Lead's Daughter - Chapter 14

An RPG gamer who played the realistic VRMMORPG ‘The Amber Sword’ for years, finds himself teleported to a parallel world that resembled the game greatly. He takes on the body of an NPC who was fated to die, and with the feelings of the dying NPC and his own heartrending events in the game, he sets out to change the fate of a kingdom that was doomed to tragedy.

- Description from novelupdates

A side story series featuring the girls of Kyoukai Senjou no Horizon.

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