PokéBase - Pokémon Q&A
1 vote

I know how to get it but why does it appear? Is there like a story to it?

its pretty much just a dead shell.

2 Answers

6 votes

SHEDINJA’s hard body doesn’t move - not even a twitch. In fact, its body appears to be merely a hollow shell. (Ruby)

A most peculiar POKéMON that somehow appears in a POKé BALL when a NINCADA evolves. (FireRed/LeafGreen)

A discarded bug shell that came to life. (Diamond/Pearl)

Shedinja's PokéDex entries have lead many to suspect that when Nincada evolves, it sheds its shell, and that shell can become a Shedinja.If you compare the two Pokémon's designs, you will see that they share head, arm and body shapes, which reinforces the theory.
The most important evidence that Shedinja is Nincada's shell is that Nincada is based partially on a cicada. Cicada larvae shed their exoskeleton when they are ready to fly — similar to how Nincada grows wings when it evolves into Ninjask. The shed shell can then become a Shedinja. The opening in Shedinja's back is in the same place a mature cicada would emerge from its shell; they are even the same colour.

In conclusion, the reason Shedinja can appear is because it is the discarded shell of Nincada. Nincada, similar to the cicada, sheds its shell upon evolution. This shell can become a Shedinja.

A nice video on the cicada narrated by the world's greatest human David Attenborough. Disclaimer, there is some mating but they're insects so it should be fine. I can remove the link if needed.

Stop being better than me.
shedinja's size is scary
he is a discarded cicada shell that is larger than my dog
Scolipede is the size of a horse. The Pokémon world is scary.
you can get lv10 salamences somewhere early on in su/mo

imagine being a new inexperienced trainer with your cute starter and your pichu and pikipek and then you step into a grass and this full out dragon just jumps you
Tell your Popplio to sing aggressively?
1 vote

To my knowledge, the games have never directly said why Shedinja appears when you evolve Nincada, but there is some evidence that Shedinja is simply Nincada's shell. For example, both Nincada and Ninjask are based off of cicadas. When cicadas shed their shell, they are able to use their wings, similarly to how Nincada gains wings when it evolves into Ninjask. Because Nincada evolving is basically the same thing as shedding its shell, Shedinja is most likely the shell that Nincada left behind. On top of that, a few of Shedinja's Pokedex entries say that it is "a discarded bug shell", which also supports Shedinja being Nincada's shell.