Now that I've read over 500 chapters, I'll give a more detailed opinion on the book. If you've read any of the author's other famous books and decided to give this one a chance, I would say that although this book has many similar characteristics, like hilarious moments and unexpected twists, it has a different vibe. At times, it is darker, and the focus on action and adventure is much more prominent.
In summary, this book starts off very well; then, the world-building and character development proceed in an interesting way, and I personally had no idea which direction the author would take. Unlike all the books I've read, the secondary characters are not one-dimensional and develop and change through interactions with the protagonist. The romance is very well developed, as we see the girl grow, develop her personality, and her feelings blossom organically.
Now, being a bit more detailed; this may contain some spoilers, but I tried not to spoil anything. If you want a general summary and don't mind knowing a few things:
In volumes 1 and 2, the foundation of the story is presented, and I found the paths taken to be interesting and fun. The author was still finding the book's tone and experimenting with things; this is natural for something different from his other works. Maybe the events were too frenetic and fast; I would easily read double the chapters with the same story, but it wasn't poorly developed, just that some might find it bothersome.
In volumes 3, the story begins to give the first hints of its direction. The book starts focusing on adventures and fights with a light touch of comedy, and the girl starts to develop her feelings smoothly.
In volume 4, a great adventure unfolds, with several suffocating moments. The new characters are excellent, and I found the end of this volume to be the best of all until then, only surpassed later by volume 6.
In volume 5, the beginning still maintains the sense of adventure from the previous volume. But then things calm down, and in this volume, the girl shines and fully develops. She is a teenager who shows her traumas, distortions, and various internal problems. Then, the protagonist has to set her on the right path. In the end, we see that little girl become a woman and the most reliable person for the protagonist. The end of the volume left me very happy and surprised.
Volume 6 is the conclusion of the big arc, where numerous problems and other minor arcs are finally resolved; or almost. In this volume, the couple finally forms excellently; we see their relationship gradually grow and become hotter and hotter. Then, finally, all the mortal world arcs, started and developed since the beginning of the book, are concluded.