By natural, I mean something like this look
, or this look
. The liner is visible, but soft. You could always blend it in, so as to soften it even more. Black is a great color for Korra.
Another option is to tightline
, which will add to the illusion of having fuller lashes and a naturally defined lash line. Make sure to curl your lashes and apply mascara.
This Korra's eye makeup is rather nice
. Her eyes are defined but not overpowering. Hope this gives you some ideas!