Tear Jerker / Kekkaishi

• Episode 4 where Yoki turns evil because of the power but still pushes Yomi out of the way of a fireball and the way he whispered her name just before he dies was heartbreaking. Makes you cry happy tears when he's re-incarnated into his small form. The ending of Episode 7, where the Patissier ghost's little brother gives him a farewell so that he can move on.
• In chapter 343, Yoshimori's mom decides to seal off Karasumori, and that can only be done if she's sealed off along with it. And the reason she wants to do it is because she believes it was the only way she could show she cares for her family. Her final good-bye to her husband is especially sad.
• The true backstory of Karasumori, Tokimori, and Princess Tsukikage. Also, the backstory of the Sousui and Suigetsu, Michiru and Kakeru.
• Almost the entirety of episode 49, which concerns Aihi's life prior to joining the Kokuboro. Her death shortly after all the flashbacks is also really depressing on many levels. Seeing Aihi's ex-lover (now an old man) and her fellow ayakashi/friend Shion retrieve some of the flowers she left behind after she died made it better AND worse at the same time.
• If you can believe it, the deaths of Byaku and the Princess are both this and heartwarming. As their world collapses all around them, they both ultimately concede defeat, embrace their ends with dignity and spend their final hours walking together, having a nice little heart-to-heart with each other and just generally enjoying each others' company as they disappear along with the rest of their world. The normally stoic Byaku even gives a genuine smile!
• There's Kouya's first death, when he's finally at peace after being killed by Madarao but is later revealed by Masamori. Before that, Kouya back when he was a normal wolf, sees his friend die in front of him.