This volume is a collection of "side stories", one of which exists just to add alternate reality scenario, such as "Yuusuke as one of the employees who was harassing Tokiko, except he sexually assaults her, but she's actually into it". Aside from that, the other stories could have been added to any of the other volumes, which makes the existence of this volume unnecessary.
I tried it with the expectation that I'd get lengthy backstories on the characters from before the outbreak or during the start of the outbreak, which would have greatly helped "complete" those characters for me. Specifically, I'd like to have seen a little bit of Mitsuki home life, how the guys from the supply division ended up together, the town hall when the outbreak started, and what really happened to the military when they were overrun.