The female Primarina and the male Incineroar are from Nintendo's Pokemon and this screenshot's taken from Valve's Garry's Mod. It is done through ShadeTheVulpix306's choice as a celebration of Pokemon Day.

They both went swimming around the ocean and it looks like Primarina just swallowed lots and lots of fish, making her belly grown into many sizes of a balloon. They then went back to the shore and Incineroar romantically hold her as she gently gives her belly a chance to settle down from such a feast she just had.