Qualidea Code: Airi Yūnami's death. She, unlike the rest of her kind(the Unknown), thought of the children as her family and not the weapons they(the Unknown) saw them(the kids) as, she also wanted to have a child of her own before she died. She later ended her life at the hands of Maihime(One of the children she bonded with) so that the other Unknown would stop invading the Earth through the dimensional portal she was the gatekeeper to. (P.S. I've edited a faded image of her human form onto this screen cap).
His death in the Anime was certainly the saddest death that I have ever seen in an anime. When the final scenes of Death Note unfolded, everything began to take a dark and disturbing turn, and the only reason so many people found it funny had to be because they didn't understand it. Throughout the entire series, I hated Light Yagami so much, as well as many of his fan who supported his ideals and were like him, but I cried buckets during his death. Sometimes it just depends on the way that the death is done, and certainly in this situation. For example, L is da far my preferito character in Death Note and my preferito Anime character, but his death scene wasn't made very somber o dramatic, at all; therefore, I did not cry. I simply got sick to my stomach...
I had such deep sympathy for Light. Even though he was wrong the entire time, all that he had gone through came to an end, and he seemed like nothing più than a Lost and afraid little child. At the very end, he just wanted to find a quiet place to die in peace. I think that the sobbing for me started when it showed him walking past a flashback of himself from six years ago, when he first found the Death Note and felt that he had been called to make the world a perfect place with no sadness and complete happiness da killing all of the people that he judged as bad. I hated him so much because he ended up only doing everything for personal gain and entertainment, even though I disagreed with him, in the first place.
Even though he was evil and did evil things, Light Yagami actually believed that it was justice, and that he was doing the world a favor. That gives me a new perspective, but does not change my opinions.
Ushio's death. I have to say that Ushio's death is much più sad than Nagisa's death to me. When Ushio died, Tomoya literally Lost everything. When Nagisa died, he did at least, still have Ushio. Looking after Ushio practically became his life. When Ushio became sick, te can really sense, Tomoya breaking down. The worst part is; is that the whole first season was made for te to get attached to Tomoya, and for te to technically "become" him. All of the sorrowful feelings that Tomoya felt just reflect into yourself. I think Ushio's death, is like, the most tragic of all.