I believe that the red crystal in the strawberry jam sword is not exclusive to the sword itself, but its actually a kind of crystal that its found either some parts of earthbread (or is produced by DE herself) and when a cookie is exposed to it they inmediatedly fall into the darkness, you can find the same kind of crystal in Cream Puff's witch costume and Wind Archer's raven costume
I mean they definitely are similar, and not to mention the trees the Churro Tribe were stuck on had red gems too, not to mention the material for Dark Enchantress’s Magic Candy, so I wouldn’t be surprised if there was a connection between these dark red gems, but I mean, there are slight differences between Cream Puff’s (mainly just the shading being a different color) and Wind Archer’s (it’s a bit different of a color) when compared to Dark Choco’s and Snow Sugar’s, which look nearly identical other than Snow Sugar’s having a red outline
Edit: I colorpicked the gem colors out of curiosity, and Snow Sugar’s and Dark Choco’s gems really are almost identical in color, with only the SLIGHTEST difference in hue. Though Cream Puff’s, not so much
Though the idea of these red gems being naturally occurring and exposing someone to it corrupts them and makes them turn to darkness is an interesting one