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Tear Jerker: ef - a fairy tale of the two.
ef: A Tale Of Memories has its share of very sad moments, in particular anything involving Chihiro Shindou's Ill Girl condition. Especially heart-breaking is the scene where Chihiro rips out the pages of her diary in which she mentions Renji, so she will forget him.
The spot that really hit this troper was when Chihiro said "I just can't not think about you for 13 hours". Then, the for a second watch through, when Renji first finds Chihiro before running off to find the pages, and she claims doesn't recognize him, you know she's acting and when you think about how impossibly difficult and heart-breaking for her to be doing that...
The scene in which Miyako fills up Hirino's cell phone with increasingly desperate messages after he stood her up on their date also qualifies—especially since all we see is her standing still and her messages written out on the screen. Pretty intense. Kudos to the voice actors, too.
A Tear Jerker on its own, but twins especially will probably be hit hard during the flashback of the accident that caused Chihiro's amnesia. Seeing poor little Kei crying in the hospital and obviously believing it was all her fault made me cry more than the two above mentioned scenes.
And for the second season, Yuuko's backstory in episode 6 (crossed over with Mind Screw) and Yuu's and Yuuko's meeting in the final episode. God dammit Yuuko, why didn't you Look Both Ways?
Speaking of not looking both ways, when Yuu finds Yuuko's body and then picks her up, carrying it with Miki? Yeah, that's bad. Then Ebullient Future begins to play. I bawled.
Yuu's and Yuuko's final farewells in the last episode. I was a little confused as to why the camera kept focusing on Yuu's eyes while he was talking about how he had moved on and would be fine without her. Then I remembered something Yuuko said in one of the previous episodes: