It's an ad for Progear no Arashi, seen in a magazine. https://twitter.com/blast68k/status/729742375879360512
madville has a keen eye, but I have no idea how you managed to trace it back to a specific tweet :O enjoy the background while you can, it's going down soon™
I figured at some point that this would happen. Ill see if there is an alternate method. The cross browser security is a huge barrier however