Suddenly, it all makes sense! Or does it? If Poniko is part of Madotsuki then...
Goddamnit, back to square one then.
On the art itself: the flat-colour style I was sure I had seen in P3 artwork before, but I couldn't find a case of it. The official website has the characters silhouetted on a flat-colour background, but the characters themselves don't seem to ever be flat-coloured. Maybe it was just some random promotional art I saw once.
Poniko and Uboa are © Kikiyama.
Evoker and Persona 3 are © Atlus.