My Sister, the Cat Vol. 1 (manga)

After losing his mother at a young age, Nekota is taken in by family friends... who happen to be a couple of human-sized walking, talking cats. Not only do his new parents have paws, tails, and furry pointed ears, but now he also has an adorable little sister, Neneko-chan! As a high schooler, he's integrated well into their household, and his precocious adoptive sister has fully accepted him as her big brother.

Whether she's showing him things she brought home from elementary school, purrsistently asking him to play with her mouse toy, or waking him up at the same early hour every morning for breakfast, life with this charming feline family is never dull!