#not that heiji or shinichi would ever die but i *really* don't like half of my otp dying so that's the first place i go ^^;

[marshmallowgoop]

What do you think would be the most narratively tragic ending for HeiShin?

One of them dying.

Shinichi becomes Conan because he does not rely on others or ask for help. (After all, if he trusted Ran to follow Vodka with him, there's no way events would have carried out like they do.) Through being Conan, he's somewhat forced to rely on others and ask for help, but when it comes to Heiji, it's really a choice. He wants to investigate cases together. He wants Heiji to help him.

So, if Heiji were to die in a case or in the fight against the Black Organization, I could see Shinichi falling back into his pre-Conan days. Relying on Heiji and trusting him got him killed. It's better to do things alone, to not let anyone in. The progress Shinichi's made throughout the series would be undone.

For Heiji, he initially seeks out Shinichi because of his own insecurities. He's subjected to tons of comparisons—to his father, to Shinichi himself—and he feels a great need to "prove" his worth.

But Shinichi doesn't do that to him. In fact, Shinichi says straight out in their first meeting that Heiji doesn't have to prove himself to him—that there's no competition in detective work. As the series continues, Shinichi also continues to support and value Heiji; he doesn't even hesitate to say that Heiji's in the right when other detectives mock and ridicule him (Episode 479), and as stated above, he asks Heiji for help (Episodes 189 and 345 for a couple big examples), signifying just how much Heiji and his insights matter to him.

If Shinichi were to die in a case or in the fight against the BO, I could see it absolutely destroying Heiji. He wasn't a good enough detective, a good enough friend, a good enough "rival," to save the Detective of the East. All his insecurities would be exacerbated.

Of course, if Shinichi or Heiji died for reasons unrelated to detective-ing, like illnesses or accidents, it wouldn't be as narratively tragic, probably, but that would be the most personally tragic ending for me, so it'd make the narrative a lot more tragic. For me.