Beheneko: The Elf-Girl's Cat Is Secretly an S-Ranked Monster!

A knight dies battling evil, only to be reborn as one of the world's strongest creatures-a behemoth. But there's a catch: he starts as a baby, and a young behemoth looks suspiciously like an ordinary housecat. When an elf adventurer mistakes him for a pet and takes him in, their fates become intertwined. She might need his strength just as much as he needs her guidance to grow into his true power.