I'm A Behemoth, An S-Ranked Monster, But Mistaken For A Cat, I Live As An Elf Girl's Pet v.1

In this new series, a knight finds himself reincarnated as a behemoth, one of the
most powerful monsters in the world, and when he meets a beautiful elf girl, he's
ready to fight at her side. Problem is, a baby behemoth looks an awful lot like...a
housecat?!