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Tear Jerker: Midori no Hibi
Midori Days with the second-to-last chapter or so. It took the entire damn series, and with tons of screw-ups, preparations, teases, training, and possibilities, but Ayase finally confessed her love for Seiji. But, Seiji stays true to Midori, having denied her love the entire time. This troper started crying when she looked up to the street light saying, "It's OK! I did it!" while crying herself.
Ayase finally works up the courage to tell Seiji how she feels... and is rejected. She leaves, laughing it off. Later, she steps into an alleyway, and breaks down crying.
What makes this even worse is that she would have fallen for him even if Midori was never on his hand, and the only reason he didn't return her feelings was because he'd met Midori first. That poor girl.
Better that Seiji rejected her up front, though, instead of stringing her along out of indecisiveness like the typical harem anime protagonist would. Or for worse reasons... * cough* School Days* cough*