Monogatari Series: Second Season

Synopsis

Returning to the present, Koyomi and Shinobu find the whole city deserted and it does not take long for them to realize that it was a consequence of saving Mayoi's life in the past. Based on the date of the most recent newspaper they found, they come to the conclusion that something dire happened during the events of "Tsubasa Cat" and return to the shrine to look for a way to return to the past. However, they find that Oshino had put a different charm that prevents them from using its powers and when night falls they are surrounded by undead beings. After escaping, Shinobu realizes that the undead were once vampires who lost their master, and that said master must be no other than herself. According to her conclusions, when Shinobu ran away from home, it was Mayoi who helped Koyomi find her, and as she did not become a ghost in the current timeline, she had never become friends with him, thus he did not manage to find Shinobu, leading him to be killed by the Cursed Cat and Shinobu starting a worldwide vampire infection before killing herself. Looking for survivors, Koyomi and Shinobu decide to use some fireworks to bring the attention of whoever managed to escape with their lives, but it ended drawing the undead to them once more. (Source: Wikipedia)