1. They really care about each other a lot
2. When Luffy becomes pirate king, he'll need a pirate queen
3. The complete each other.
4. Luffy trusts Nami more then anyone else. He even gave her his hat which was his most prized possession.
5. They always save each other and look out for each other
6. Danny and Layosas stories. Reading those made me like Luna even more.
7. They are a really cute and funny couple.
8. All their moments in the strong world movie.
9. Luffy makes Nami happy again
10. They are just a perfect couple