Tasteful character deaths can be a great source of plot development. However, when a series botches a supposedly tragic death, it leads to unsatisfying narrative arcs that make you shake your fist at the laptop screen.
Some of the worst anime endings in history are caused by characters who died too soon, as a hero's untimely demise inadvertently closes the door on potentially fascinating plot lines.
In Death Note, L's connection to the villainous Light Yagami deepens significantly just before his death. He goes down right as things are starting to get interesting, so much of his character development feels wasted.
When a character dies prematurely, it's difficult not to think about what could have been.
Before his death, Shiro Fujimoto (Rin Okumura's adoptive father) was a top-notch exorcist who could go toe-to-toe with almost any demon, except for the actual Devil, Rin's biological father. This dude not only refused to kill Rin and his brother Yukio, he also raised the sons of the Devil himself, defying orders to do what he thought was right.
Isn't Fujimoto a great guy? Unfortunately, viewers only get to see him in action for a few short episodes before he dies. His death itself is epic: he's possessed by the Devil, his adopted son's true father who is attempting to drag Rin back to Gehenna, the anime's version of Hell. Fujimoto ends the possession by stabbing himself to death, a ridiculously heroic act that befits this awesome character.
His death was too soon, not because he should have survived his fight with the Devil (his sacrifice was actually really cool), but because it was so unfair that he'd had so little screen time beforehand.
L Lawliet's death marks the moment when a lot of fans stop watching Death Note. While there's some cool material in the second half of the show, L's absence leaves a gaping hole that never gets properly filled.
Over the course of the series, L and Light Yagami develop a surprisingly intimate bond that complicates their mutual desire to eliminate one another.
After Light successfully kills L using the Death Note, the eccentric detective is quickly replaced by Near. While fans are divided on whether Near is a good character, he definitely doesn't possess the same connection to Light as his predecessor. When Near finally succeeds in taking Light down, his victory is way less meaningful than L's would have been.
Kaori Miyazono suffers from a terminal illness, so when she dies, it's not really a surprise. Even so, her demise comes far too early, as she never gets the chance to admit her true feelings for Kousei Arima, or to find out whether he feels the same way.
This could have been the most satisfying moment in the story. Instead, the eventual reveal only adds to the tragedy, as it comes after Kaori has passed away.
Marco's death isn't explicitly shown, so when the Survey Corps finds his body after an intense battle with Titans, viewers learn nothing new.
Not only does Marco's demise add little to the lore of Attack on Titan, it actually inhibits some potential plot lines that might have been interesting. Viewers don't get to see Marco's budding friendship with the prickly Jean Kirstein come to fruition, and Marco never succeeds in becoming a positive influence on the Survey Corps.
Marco's idealistic views could have changed the organization for the better, but instead, he's just another corpse on the Titans' hulking pyre.
*Update for Season 3*
Turns out that Marco's death is actually explained during a flashback. He still died too soon though!