This image is printed on some kind of tarp, and it's huge! It's almost 4 feet by 6 feet (1200 mm x 1800 mm). It's from Advanced Generation, and features every Pokemon up until that point in roughly numerical order from left to right. It doesn't say the manufacturer in the corner, and the reverse side is simply white. It did come MIP, with a sheet of paper with some info on it. All I gathered from that was that it's made of polypropylene, but my Japanese isn't very good.
What is this tarp thing? Who made it? My best guess is maybe it's a kids' mat used for hanami or something, but I really have no idea. Any help is appreciated.
More pics under the cut:
The verdict: General consensus is that I have a picnic/leisure mat from Seibu Department Stores! After doing a bit of digging, mine seems to be unusually large for this sort of mat... But it definitely appears to be one. Thank you for the help, everyone!