Yuusuke was a shut-in with a dislike of other people, until the zombies appeared. Fortunately for him, for some reason they wouldn’t attack him.
As he was exploring the zombie-infested town, he came across Mitsuki and her brothers holed up in a supermarket and started living with them.
Just as they were adjusting and feeling happy with their new life, an unfortunate incident occurred that spelled the end of their time in the supermarket.
Instead, they took flight for the town hall, where they’d heard the rest of the survivors had taken refuge.