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Tear Jerker: Kami-sama no Inai Nichiyoubi
In the first episode alone, Ai loses her entire village after Hampnie massacres everybody, and one particular zombie proves his inherent humanity by trying to protect Ai from Hampnie; underlined by the fact that Hampnie was targeting the zombie over Ai, and thus he had reason to abandon Ai. The zombie gets headshotted twice for his troubles.
The scene in episode 3 in which Ai cries after having to bury her father, Hampnie Hambart, qualifies as one hell of a tear jerker. Hampnie dies shortly after discovering that he is Ai's father, and gets to spend a final happy day with his daughter as an undead, before being buried for good by Ai, who is brought down to tears during the ordeal.
The end of the Class 3-4 arc. Alice and his classmates finally remember what drove them to trap themselves in a "Groundhog Day" Loop, and he says goodbye to them as the world is disappearing. Ai, crying and begging him not to disappear, embraces him, but after he kisses her forehead he pushes her back into the outside world. Afterwards, all those tears become tears of joy (and possibly confusion) when we see Ai at Alice's grave, and then he comes up next to her, revealing that Ai had wished for him to be able to continue to exist in the outside world.