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Tear Jerker: Cross Game
The first volume/episode, and how. Kō's final line (It's so simple... I just need to cry) is just crushing. The ending song is extremely sad, too, since it's essentially all about Kō and Wakaba's relationship, and, well, yeah.
And all reminisces by Ko, Aoba, and Akaishi back to "that day/summer," Wakaba, and her last dream.