I Walk Among Zombies Vol. 0 is the final release in the series and contains a series of short scenarios featuring the main characters in the series.
Take a step into the shoes of Mitsuki, Tokiko and Sayaka and learn a bit more about their circumstances as well as their interactions with the protagonist in these short stories that take place in around each of the games in the series.
It’s recommended to play I Walk Among Zombies Vol. 1-3 before starting Vol. 0.