Supreme Casanova: Ultimate Harem System - Chapter 306: Freaky Ones.

This is the story of a person who transmigrated into a world with a radically different worldview.

Cote: There is Something Wrong With HikigayaBy: XiaokoPatient Profile:Patient: Hikigaya Hachiman, Year 1 Class D, Tokyo Metropolitan Advanced Nurturing High SchoolDiagnosis: Adolescence SyndromeCondition Overview: The patient claims to have woken up in a parallel world, where both his physical age and relationships have drastically changed!Yukinoshita Haruno is now his classmate.Shizuka-sensei is somehow teaching at Sobu Middle School...And before he knows it, he ends up in a prestigious school with a 100% graduation and employment rate, stepping onto a fate that even destiny itself cannot predict!

Due to an unexpected turn of events, Xia Fei consumed a Super Gene Optimization Fluid that bore no brand, expiry date, instructions or stated its place of origin.
Our story begins here…

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