What in the Crest is This?!

So , we have now found some weird items, that may or may not be related to the Crests were a part of. For now, I'm just going to list them:

Black Ring
Red Gem
Blue Gem
Yellow Gem
Ancient Scythe
Blue Ring
Yellow Ring

Now, I'm not even sure whether they names I have just given them are their real names, or what they are used for. In fact, I have no idea where they came from... Does anyone have any clues?