A peak melodrama prequel story about Miho's past that had been hinted at here and there in the main series. It doesn't introduce much to the series overall, and it only makes Miho's past a melodrama filled with angst. Just like the main series, you do see Miho making friends and becoming a tank crew at lightning speed, but the subsequent relationships aren't as stable as the main series. Instead, you're introduced to several drama-fueled conflicts between the characters you just saw, all four of the entire crew, in fact, over the short eight chapters that the series has. Each don't really mean much by themselves,and it's only at the final arc where someone in the crew has to leave the school, and when Miho has to confront her sister about the summer tournament.
The manga just adapts the prequel story in a shallow manner.