This item was described only as a "Prize Card"
It's from 2015 (which you can read there in the orange oval) but what is it, exactly? It came inside this tri-folded paper, possibly a brochure or maybe a letter. The card itself seems to be plastic, and fits in the lift-a-flap paper holder stuck to the larger paper. It features CG Sonic, some blue sky & colored balloons. The letter & card text are all in Japanse though, so you can't really read it to see what it's about. Do write in with details for credit, if you can shed some light on the card/letter purpose!