Crystals: the one thing that holds an even greater sway on the war between sekkians and taints than any of the dragons or humans could try to do. They are, in essence, what bonds and breaks the dragons and riders, and what can be the strongest asset, or the weakest link for them.

What are the crystals?
The crystals are magical stones that grow naturally within every dragon; in modern times there can never be a dragon without a crystal, as they double as a bonding agent between the humans and dragons and a magical circuit for the dragon.

How do the crystals come to be?
A crystal is formed as a dragon develops within the egg, and is always on a visible portion of their body, though can be placed anywhere.

Likewise the crystals that are given to the humans during a hatching are made by Kazuko through magical means (though as of yet unknown means, she has thus far refused to give an explanation of how she is able to create them). However it is assumed she is able to read the magical aura given off by the growing dragon, and is able to 'see' the crystal growing within them; and with that information she is able to magically replicate each crystal to match the one within the dragon's body, and from there on out she is able to hand the crystal out to the human the baby dragon has chosen.

Are crystals the same?
No, each crystal is unique to the dragon and rider pair, there have yet to be two exactly the same, they can be any shape and color. The crystal can vary in size, but usually is the proportional size of the owner's fist, however some can be larger and smaller, variation is the key.

What happens if a crystal is broken?
If a crystal cracks, fractures, or breaks completely, the taint then seeps in through the broken magical circuts, which then mutate the dragon and rider, should either of them survive the cracking of a crystal.

Given the capture of Nidhogg, the Taint is no longer capable of breaking in. However, the crystal is still the conduit for the bond, and as such, damaging it weakens the bond between a dragon and rider. The destruction of the crystal then destroys the bond between the two.

How can a crystal break?
The most common way for a crystal to break is from a direct impact due to the war on Sekkai. Due to the crystal cracking forming taints, the tainted forces have started to target the crystals instead of instantly going to kill their enemy, as to gain more numbers.

However a crystal will also break should one half of the partnership die. So if a dragon's rider dies, the crystal on the dragon will break, and the dragon will taint; this can happen the other way around, but is much more rare and less spoken of. This is due to a tainted dragon being a useful tool in attacking other dragons, a human cannot do much damage to dragons.