Anime where humans have robotic creatures and power them by crystals

I saw this anime on YouTube some years ago, I remember that its name was one word but maybe it was just named like that to not be removed from YouTube.

In the first episode, I think that the main character (a young boy) either arrived from another word, or had amnesia, I’m really not sure on this one.

In this world, there are creatures (who look a little like robots if my memories are not wrong). They need to have a human with them to work.

To use their powers, these creatures need crystals with different colors, the main character (his creature looks like a lion) uses red crystals, they’re hanging to his belt. I also remember that another character with a dragon (black or purple, I’m not sure) used purple crystals located on one of his gloves.