Dark knight lore questions. help

[Aerazen]

I wonder when it comes to dark knight.
Darkness within them does it actually manifest.
When you use few of their ability it like they shoot a consentrate beam of darkness?
So does it work like aether for the magic classes?
Like is darkness a type of magic they use or is it just in them.
Like in their mind and not actually there.. so they just put it there in animation for show but not in lore?

[Anonymoose]

If I properly understand what you're asking, yes, it seems to exist outside of the DRK's head.

As the fight wore on, it began to soak through his armor, spreading to every ilm of his body. But when it began to rise and envelop him as a mist, I realized it wasn't blood, but something dark and twisted...

This was likely Darkside, which Fray explains is similar to magic while warning that energy sourced from dark emotions can consume you:

Now, should things turn violent─as I expect they shall─you may need to tap into your darkside to survive. It's not unlike drawing upon your own aether to weave magic. Fear, pain, rage─that which lies in the deepest depths of our soul makes for a potent fuel.

To go off on a digression...

The mythology states that Hydaelyn and Zodiark once shared the aetherial sea; Darkness (capital D) seems every bit as aetherial as Light, down to the existence of Darkness crystal and Darkness sprites. Just like Paladins and White Mages can harness aether in ways that that seem to tilt towards the Light, it seems as though the Dark Knights can do the same in the opposite direction.

However: the darkness mentioned in reference to Dark Knight is lower-case. It seems to be a poetic darkness within. Does the fact that we still see Darkness auras and Darkness sprites and Darkness-based abilities hint at a Darkness within (a la Promathia and Final Fantasy XI)? We can only speculate, as we have been for a long time. (Thanks, Ramuh.) Thankfully, it doesn't seem as though your query requires going quite that deep!

To the contrary, NPCs (such as the Moogles) don't seem to believe that Dark Knights do much more than harness their own emotions (as Fray hints at right off the bat). They are allowing the pain and anger that is born when justice and love are abused to become a furious and tainted source of energy. Even Sidurgu comes around to believing that these dark emotions arise from desire to protect that which we hold dear. The "flame in the abyss" of which his master spoke is that very passion. The fact that he was using Rielle as an excuse take revenge on Temple Knights for murdering his family blinded him to the role that his affections (for both his family and the girl) were playing in his harnessing of that darkness. Again, it doesn't seem much different than a Paladin's energies manifesting as if they tilt towards the Light.

Perhaps, as in all things, man cannot invite Light into his heart without it casting a shadow.

[Cilia]

Now that I'm at my desktop and not working off my phone...

Long story short, the power of "darkness" is a manifestation of your own heart. Since all hearts have some measure of darkness in them, however... you shoot darkness energy.

Unlike mages, Dark Knights do not draw aether from their surroundings at all to fuel their powers / spells. It all comes from within, which is why certain abilities require Darkside active and Darkside itself will cut off if you drop to 0 MP as a safety measure. Blood Weapon and Blood Price allow you to recharge through hurting others or being hurt yourself, respectively.

Yes you literally shoot beams of darkness and stuff. It is a form of magic, but very dangerous, requiring a strong emotional state and will to keep yourself from burning up on the power of darkness. Aside from the fact everything else related to darkness on Hydaelyn is evil, that's why Dark Knights are feared and reviled - they will go to any length, pay any price, not for orders or oaths but for their own convictions. Such people wielding such power can be... very, very dangerous.

[Belhi]

I was going to answer but Cilia will probably give a far better explanation.