Belly button fetish is badass.
Firstly, wearing a crop top in any weather or activity is cool. Like, "I don't care if I'm cold or people stare, my belly button is going to be exposed". Secondly mermaids are cool and they usually show their belly buttons. Third, belly button piercings are cool. Fourth, there is a Japanese myth that a thunder oni will steal your belly button if it's exposed. Because of this, exposing your belly button is associated with onis and thunder. Both are cool. Fifth, the Arabian nights aesthetic is cool, Arabian nights aesthetic means a lot of exposed belly buttons.