For this I definitely have to say Anohana (aka We Still Don’t Know the Name of the Flower We Saw That Day, Anohana: The Flower We Saw That Day, and Ano Hi Mita Hana no Namae o Bokutachi wa Mada Shiranai). Considering the anime focuses on a boy by the name of Jintan seeing the ghost of a girl named Menma, who he was close friends with as a child, it’s the obvious choice. The anime takes a pretty in-depth look out how death affects different people in different ways, including the group of friends at large, and Menma’s family. [SPOILERS from here on out]. In particular, Yukiatsu’s reaction is heart-breaking; blaming himself for Menma’s death and dressing up as her on occasion as he is haunted by her death. When Menma returns to her home to see her family (who can’t see her) is another sad moment, and really draws attention to how people move on after death. Even small scenes, such as Jintan freaking out when Menma disappears from the bridge, thinking she has drowned again, are quite sad in the context of the entire anime. And then you get the ending, and it is tragic. The friends not wanting her to go, Menma trying to hold on to say goodbye this time, writing out notes to everyone, and then finally disappearing in the sunrise. I’m tearing up just thinking about it. This is a beautiful anime, but it is certainly a sad anime.