I was watching Fairy Tail the other day and I was like, hey why does Happy have wings? He's a cat. jeez. also, like, how can he fly Natsu around? He's puny.
Because Happy isn't a cat, he's an Exceed and his wings are a result of the spell Aera which Exceeds have.
Aera (翼エーラ Ēra): Happy is able to sprout angelic wings that give him the ability to fly and carry objects or one person at a time for a specific amount of time.