Mayoi Jiangshi, Part Three Episode 9

A woman appers to drive out the undead by throwing rice at them. Much to his awe and joy, Koyomi learns that the woman is none other than Mayoi herself, bringing him a letter from Oshino, who somehow figured out the whole situation. From the letter, Koyomi and Shinobu learn that they had traveled to a different timeline and before they return to their unchanged, original timeline, he asks them to confront Shinobu's alternate self who is still alive, and must be destroyed to stop the undead plague and prevent the world from being destroyed for good. After bidding farewell to the adult Mayoi, the pair return to the temple ruins and meet the alternate Shinobu, who cries of joy upon seeing that in another timeline, she managed to reunite with Koyomi, and offers to sacrifice herself to allow them to return to their own timeline. Back to their own rightful time, Koyomi realizes that he missed the opening ceremony much to his chagrin, and after Shinobu returns to his shadow, Mayoi appears before him, and they take their time as they walk together to his house in order to return her backpack.