Girls und Panzer the family secret a story of the Western Front

A teenage boy was visiting his grandfather who he barely knows about him. When he arrived he asked if he can search in the Attic for anything that could be sold in his own yard sale in hopes of getting enough money to buy a new tank in which his grandfather said yes but only if he has the final say on which stuff that could be sold. After he enter the attic he noticed a photo in which in it was a group of boys and girls together but what really caught his eye was the fact that in the background behind all the boys and girls was tanks marked in the old mark of the school Kuromorimine in which they were defeat during the World war II the second in which he started to look more closely on the photo and noticed a signature on the back that looks like his grandfather hand writing so he came downstairs with the photo to asked him a question about this photo.