So Evansi's world is like 90% water, and rather than having continents, they just have many, many clusters of islands.
Her version of "Manhattan" is basically built on the peak of an underwater mountain that broke the surface of the water. The rich used their vast wealth in order to build into the mountain walls under the water, developing technology like masks that would filter oxygen out of the water, submarines, and gear that would help them get around from place to place faster.
Meanwhile the lower classes have to stay mostly on the rather overcrowded mountain peak, since they can't afford those masks.
This means that while the upper class and upper middle class are able to spread as far as they want and go wherever they want, everyone else is just kind of stuck having to deal with the difficult mountainous terrain and the tight space restrictions.
Many people do commute back and forth above and below water for daily jobs, using submarines that basically function as buses. However, they are unable to travel freely underwater and can only remain within the buildings.
Evansi does have her own Mary Jane! She's a singer and routinely performs at a famous club.
Her civilian name is Rowan Rivera and she's a college student majoring in dance (what kind of dance? ...Idk yet.)
Edit: Changed her last name