>>279762272
>Asa does good things for good reasons
The manga states Asa can't really tell right from wrong, her character is very similar to Denji's, but with the sensibilities of a teenager girl instead of a feral boy.
But you're right in the way they are meant to complement eachother, and that is even reflected on their designs.
>Asa: black hair, pale skin, blue-grey eyes, cold, timid, cat
>Denji: blonde hair, tan skin, red-ish brown eyes, warm, vibrant, dog

>>279762366
The difference though is that unlike Spider-Man writers, Fujimoto doesn't dislike Denji.