I am Behemoth of the S Rank Monster, but I am Mistaken as a Cat and I Live as a Pet of Elf Girl.

In a twist of fate, a knight, after falling in battle against evil, is reborn as a behemoth, one of the most powerful monsters in existence. However, his baby form resembles a house cat, leading to a comical case of mistaken identity. Instead of being slain, he is rescued by a beautiful elf adventurer. Now, the knight-turned-behemoth lives as her pet, navigating a world where his true nature is a secret. This unusual premise sets the stage for a journey filled with confusion and unexpected relationships. The story explores themes of identity, the contrast between appearance and reality, and the unlikely bonds that can form between different beings.