It's not common for Toei to kill a hero, but there are some out there. Some of them are great example of a proper build up, while others comes in as a real rushed work. I'm going to classified the ones who happened in their respective series AND stayed dead once it ended. Finally telling why I think they belong there. This is my opinion
Why I think they belong in this category? Because of the writing or the message belong it.
Let's see: we all know the story behind the scenes of Dragon Ranger. For the ones of you who don't, I'll recap it from memory, so forgive me if I say something not completely right. After the introduction of Burai (and I think already established he was destined to die), Toei received bags and bags of letters from the audience begging them to find a way to not kill the character. Toei discussed it with the writers and went along with the original idea the staff had. They did that to teach the kids heroes can die too! Great message if you ask me. Not everything has to be like they want. Life lesson :D
On the other hand we have Black Condor, who during the course of Jetman faced/died many times. And I think his ultimately death was well craft. Even if the other Jetman were in the same position as Gai, every experience he had helped him to explain how was possible for him to be at the Legend War (and the Jetman tribute episode in Gokaiger). I really love that for 19 years, most fans were discussing if Black Condor was dead or not. I didn't need Gokaiger to tell me that in my first time watching Jetman.
AbareKiller and Beet Buster shares the same kind of writing. They're both destined to die since their first episode, but the writing were completely different. Their background stories is what makes them being among the best writing deaths. The way they were executed was handled differently and that's what I love of them.
Battle Cossack I
Mele & Rio
Why I think they belong in this category?: Their writing was ok. Nothing impressive to emotionally move me but it's not horrible as to despise them. Maybe Bull Black might be a bit silly, but I think there were worst. They die trying to save a cause, I don't see anything bad on doing that.
Yellow Four I
Why I think they belong in this category? Merely because of the writing/timing.
Let's see: Gosei Green only lasts onscreen 5 minutes, no build up to know the character, no mention of him previous or after the episode. He's there to say, "Hyde had a partner but he was killed trying to save his kind and humans." Give Hyde a driving force and nothing more. Ok, I get he's not the protagonist of the show, but at least, if the writer wanted to tell us something about Hyde and how equal he was before , they could at least dedicate most of the episode on both characters. How they were like, how he died. Definitively Not what we were thrown our throats.
Time Fire's death is pathetic to say the least. Dying over returning a bird to a little girl? Ok, I get it. Wanted to show the human part on the character. Failing to notice a single minion? Inexcusable! Nothing more to say.
Yellow Four I is lame for the timing, though it's not the writers' fault. Yet, I think it could be handed better. Let's see: the Biomen are all scattered around doing their thing, Mason attacks Yellow Four, she transforms and is hit with the Anti-Bioman particles. The others get the notice, meet with her and start what we see in the episode. See? I made the episode a bit better. Now, you may think I need the actress to play it right? No, because the camera would focus on the character once she's transformed :P Least to say, Yellow Four I's death is bittersweet because it occurred earlier in the series unlike with the other dead senshis in this post. What a shame is the fact she was one of the protagonist of the show (unlike Gosei Green).
To sum it up: I believe doing a hero's death is not an easy task which can turn out to fit in one of the three categories displayed above. Death is at its best when the story goes that way or when there's a collab between the writers and the actors (best example is Black Condor from Jetman). Death is ok when it's a complete surprise but the hero dies trying to do his/her job (best example is Kiiranger II though I find Battle Cossack II's intro ep is better handled). Another ok is when a bad guy dies trying to redeem himself (always considering he/she was destined to die since episode 1--best examples are Mele & Rio from Gekiranger). Dying is at its worst when they make the character idiotic, even though it was not what they were aiming (best example is Time Fire from Timeranger). When the character was never mentioned before and only appeared on-screen 5 minutes and it's never mentioned again. Why bother to create a character with that conditions? I top this kind of death as the winner if there were an award for "Worst Death Writing in History". No excuses. And if there was an award for "Lame Death Writing in History", I'd choose the killing a main character early in the series with a smart plan not fully developed at that time.
What do you think? Do you agree with me? Do you think I'm picky? What do you think on Death of Heroes? Do you like them?