Kasei Zombie

The story is set in Tokyo's Takadanobaba neighborhood, and follows a girl named Kanon as she confesses to her upperclassman Akiyama and goes on a date with him to see a movie he wanted to see, titled 'Kasei Zombie.' While she is in the bathroom, there is an earthquake and she is trapped. When she finally escapes, she finds that Takadanobaba is overrun with zombies and has been blockaded off. Then, she meets a man in a blue helmet who fights zombies with a bat.

(Source: Anime News Network)