As described on the official twitter account:
This is a space where you can talk alone to the idols. You can experience different topics and conversations than you see on the home screen. Depending on where you tough them, and how often, you might get special reactions from them...?
a little bit of info for those who don’t know : these drawings are based on a ask I sent @teecupangel about Des being turned into a slugcat, with the ability to change forms into different slugcats when certain criteria is met. His default form is survivor.
for example The Monk requires close contact with a loved one (usually an ancestor or clay) to be switched to. While The Hunter is utilized when stealth is needed, like stalking a target.