Well, in the Pucca comic, 'What's yours is mine' could suggest a theme of chaos or lack of respect for personal property. It could be part of a storyline where characters have this odd belief that leads to conflicts or funny situations.
I think in the Pucca comic, 'What's yours is mine' could represent a kind of mischievous or rebellious idea. Maybe it's a catchphrase for a particular character who likes to cause trouble by claiming other people's stuff as their own.