One Piece - I Am A Different Luffy! - Chapter 5 - 4 - Koby.

Beast Taming: I Can Evolve Indefinitely

Su Hao awakes to a greatly changed world. Even vegetation and mountains can become sentient. Even an antique saber can produce a sprite? There are other subjects in education? Being a Sprite Trainer is the most popular job?

Just when I got to know her, the hairy girl only wants to beat me up!Prim childhood sweetheart treads on me underfoot!Childhood friend turned sister suddenly demands I repay the kindness of upbringing?...Are all these twists of human nature, or the moral decay?Surrounded by young girls wielding knives, Shen Mo Dust trembles: 'Author, why do I only meet bad women?''What exactly are you not satisfied with, let's switch roles!'Jealous at having crafted the protagonist's peak of life with his own hands but without a single girl by his side, the author furiously slams the keyboard!(Spotting the little whips raised by the venerable readers, he picks up the keyboard again)The alternate titles of this book are 'They Shine Like Stars' and 'They Are Lonely Like Stars'.

Another entry in what you can call the Proto Harem Series: the books written before the Harem Series that take place in the same world.

It’s about a swordswoman whose student is captured, so she goes to rescue her.