Viewers in Mourning

Fans can be a strange lot. They get really invested in the show they are watching, they come to empathise with and care for the characters. They come to see them as friends. Sometimes this gets taken to a strange place.

When a fictional character dies, there is often a very emotional response. In fact it can often lead to the sorts of public displays of affection that we might expect for a major public figure.

This can either be a sign of a great writer, or a terrible one. Either the death struck a cord deep and meaningful or the fans become enraged that They Just Didn't Care.

As this trope is about reactions to character deaths, here be spoilers.

Examples of Viewers in Mourning include:

Anime and Manga

A real life funeral was held for Raoh of Fist of the North Star. Though it was more of a publicity stunt.
From The Other Wiki on Ashita no Joe:

"When the fans of the series saw the death of Rikiishi, there was a special funeral for him. In March 1970, about 700 people packed the streets dressed in black, wearing black armbands and ribbons with flowers and incense, participated in the funeral. The event was called for by poet Shuuji Terayama. The service was conducted in a full scale boxing ring watched over by a Buddhist priest."

A lot of Tengen Toppa Gurren Lagann fans were heavily affected by one of three deaths: Kamina, Kittan, or Nia.
When the Sailor Scouts die in the two-episode finale to the first season of Sailor Moon, children in Japan were so upset by this that they made themselves sick.

Comic Books

When Superman (temporarily) died, a lot of fans went crazy with apparent grief. Despite the fact he's a Comic Book character and it was therefore inevitable when he came back to life a few months later.
- Given how broad Superman's sphere of public awareness, most of the mourners were non-comic book fans, while the Genre Savvy regular readers were more shocked that they actually did it, still it's a mark of how much said savviness has grown over the years: Superman's death made national news. Batman's death, fifteen years later, went mostly unnoticed outside of the DC readership. There was still some interest; if any superheroes can breach the mainstream, it's Superman and Batman. Captain America's assassination made a few ripples, too.
When Flattop, a villain of all people, finally died in the original Dick Tracy strip, fans staged a funeral for him.

Film

When Godzilla vs. Destoroyah premiered in Japan in 1995 and Godzilla died, a huge funeral was held for him on national television with many of the people behind the series in attendance. Even CNN was abuzz about it.
While the Browncoat fan community was very pleased to have a follow-up movie made of the short-running TV series Firefly, director Joss Whedon's decision to kill off Wash, one of the most popular characters, who should have had Plot Armor, ultimately ruined the joy of having Serenity for many fans. Shepard Book's death, while also sad to many, had a muted reaction at least in comparison, probably since viewers usually get fixated on a single character.

Literature

Young men in London wore black mourning bands on their arms after Sherlock Holmes died in "The Final Problem." Then they made Conan Doyle resurrect him.
When Sienkiewicz Trilogy was originally published, the death of Longinus is said to have inspired a similar response. Old pious ladies asked for masses to be held for the peace of his soul.
The death of Little Nell in Charles Dickens's The Old Curiosity Shop.
Sirius Black's death in Harry Potter and the Order of the Phoenix caused extreme grief in the fanbase—a popular avatar/signature saying shortly after the book's release was "JK took my love away; I am still in mourning." The fact that his death was never really explained, as it involved magic only seen in that scene, didn't help.
- Some fans were vocally unhappy when Dumbledore died in the following book.
- Not to mention Fred, Lupin and Tonks in Book 7. Oh, and Snape due to his role in everything.
Older Than Steam: Richard Barber, in his The Knight and Chivalry, notes that people used to get really emotionally invested in Chivalric Romances (the ones parodied in Don Quixote) and recounts a 16th-century anecdote about a man who returns home, only to find his family in tears and despair. He asks them if anyone died, and they answer that, indeed, Amadis Of Gaul (a protagonist of a particularly popular romance) did. Even if it's just a joke, there were also recorded real-life cases of people swearing by the Bible that their favorite romances actually happened, so such mourning, comparably mild, was probably quite frequent.
Hercule Poirot's obituary was at the front pages of the New York Times (August 6, 1975).

Live-Action TV

When Ianto Jones died in Torchwood, a spontaneous memorial was constructed by fans outside the supposed entrance to Torchwood where it remains to this day. They also raised a lot of money for charity in memory of Ianto.
When Mrs. Landingham died on The West Wing, she was eulogized in Congress.
Daniel Jackson's first real death in Stargate SG-1 didn't make the fans sad - it made them downright angry! So they made a website and eventually got him back.
- Then the Atlantis writers thought they'd do it again with Beckett. Beckett's fans actually donated a large amount of money to a Save the Turtles foundation in his memory after the character had mentioned liking turtles once. He too made his way back to the show.
The death of Maid Marian on the BBC's Robin Hood was met with abject fury, a flood of complaints, and a lot of suspicious behind-the-scenes dealings (including the resignation of the writer and co-creator who wrote the episode in which she died). The writers/producers seemed to have realized just how spectacularly they fucked up, as the third season was given little publicity and a terrible time-slot, and after the ratings dropped exponentially the show was duly canceled.

Radio

When Grace Archer died in The Archers a surprising amount of people sent her husband flowers and condolences cars care of the BBC.
- The Grace Archer story was parodied in a TV episode of Hancock's Half Hour. The producers of Hancock's radio soap are delighted to have got rid of him until they realize how much public grief his character's death has caused, and then he has them over a barrel.

Video Games

Aeris' death in Final Fantasy VII caused this, to the point that many people were desperately hoping that there was some way (or point) she could/would be revived, even to this day. This was a particularly effective one, partly due to how far technology had advanced in gaming (making the death scene even more poignant) and partly since the writers actually set out to invoke this reaction (they succeeded...a little too well, some might say). Other Final Fantasy games before and since also had this response at times, but Aeris's to this day remains the strongest.

Web Original

Happens a LOT in Homestuck. In general, at least one of the deaths in the series will get to you. People have had mental breakdowns because their favorite character died. Fans certainly are weird.

Western Animation

When Optimus Prime died in The Movie, young fans were crying, and sent letters asking for him to return. The fact that most of the previous cast also died apparently didn't effect them as much.
- This actually ended up causing some Executive Meddling in the G.I. Joe movie that was about to be released soon after, originally Serpentor was going to kill Duke, but after the fan reaction to Optimus' death they quickly dubbed in a few lines saying he was only put in a coma instead.
- During Beast Wars, it was Dinobot's Heroic Sacrifice that hit the fans hard.
Season 4 of My Little Pony: Friendship Is Magic saw the Golden Oaks Library destroyed in a fiery explosion. (It Makes Sense in Context.) The reaction of Bronies around the world can be summed up in the hashtag #SaveTree2014.