I'm looking for a One Piece Doujin novel.

It was a One Piece novel. It was a system novel. The main character could use the system to extract the bloodline of various anime planes and fuse it with a beast. After the fusion was successful, he could even change his form. He could take the form of an animal or a human. After that, he would cooperate with Bergeroponk to fuse with a guy similar to the Four Emperors Kaido. He was very powerful! There were many who were very strong after combining many strengths. There were many who had the strength of a general and the strength of the four emperors.

Answer 1

One Piece Doujin novel recommendations are as follows:
One Piece: Golden City

The novel told the story of Luffy and the others in the Golden Nation. The Golden Nation was a mysterious place with powerful Golden Fruit ability users. In the Golden Nation, Luffy had encountered many interesting characters such as the Golden Princess and the Golden Warrior. The plot of the novel was complicated and the characters were rich. It was a very exciting One Piece Doujinshi novel.