Are there any novels where the protagonist is reincarnated as a monster and has to become stronger?

Yes, absolutely! This is a very popular subgenre on Novelblur, and there are tons of fantastic stories where protagonists find themselves reborn into monstrous forms and embark on a journey of growth and survival. It's a compelling premise because it immediately throws the character into a world of disadvantage and forces them to adapt and overcome their limitations.

One of the most well-known examples that fits this description is "Re:Monster". In this series, the protagonist is reincarnated as a weak goblin and possesses a unique ability that allows him to gain new skills and powers by eating. He has to strategically hunt and evolve, starting from the bottom of the food chain and gradually becoming a powerful leader. The progression is incredibly satisfying as you witness him go from a helpless creature to a formidable force, all while dealing with the challenges of his new existence and the inherent prejudices against monsters.

Another excellent choice is "That Time I Got Reincarnated as a Slime". While not strictly a "monster" in the traditional sense at first, the protagonist is reborn as a slime, a creature often considered weak and insignificant. However, he quickly discovers he has an extraordinary array of skills and abilities, including the power to absorb and mimic. This allows him to evolve and grow in incredible ways, eventually becoming a beloved and powerful figure who bridges the gap between humans and monsters. The story is full of adventure, world-building, and a strong emphasis on the protagonist's growth and the relationships he builds along the way.

You'll also find variations on this theme where the reincarnation might be into something more traditionally monstrous, like a dragon, a spider, or even something more abstract. The core appeal always lies in the struggle for survival, the discovery of latent powers, and the moral complexities that arise when you're not human but have human consciousness and desires. These stories often explore themes of identity, prejudice, and what it truly means to be strong, not just physically, but also in character. Keep an eye out for tags like "monster protagonist," "reincarnation," and "leveling system" when browsing the fantasy sections, and you're sure to find many more gems!