Shardbearers are known to be extremely powerful warriors, easily having the strength of several men. They also have increased speed, stamina, and resilience, setting them apart from average soldiers.
They need space to fight; their Blades are so long that hurting one's companions is a very real danger.
Shardbearers are destruction incarnate, the most powerful force on a battlefield. They are considered to be beautiful divinity in battle. They aren't just a force of destruction; they are a force of morale and inspiration. They change battles.
In Dalinar's first vision, he fights the monsters of Midnight Essence (as Heb), then - looking upward in a painful moment, sees a brilliant blue light falling through the air. He cries out as the light hits the ground a short distance away, and watches in amazement as the light stands up, limbs unfolding. It is a man (i.e., Harkaylain) in glowing blue Shardplate, bearing a Shardblade, trails of Stormlight rising from his body.
The man raises his Blade and strikes with skill, stepping into his attacks on the monsters. Dalinar lies stunned. This Shardbearer is unlike any other he has ever seen. The Plate glows with an even blue light, and glyphs - some familiar, others not - are etched into the metal. They trail blue vapor. Moving fluidly, Plate clinking, the man strikes at the beasts. He effortlessly shears one in half, flinging pieces into the night that trail black smoke.
After the attack on the monsters between the three of them - and the female Shardbearer's ministrations, the male Shardbearer addresses Dalinar and says that he's never before had the pleasure of fighting alongside a comrade with such unconventional means. He stands with his Blade resting on his armored shoulder, inspecting Dalinar with eyes of such bright blue, they are almost white. Dalinar wonders whether those eyes are actually glowing, leaking Stormlight. His skin is dark brown, like that of a Makabaki, and he has short black curly hair. His armor no longer glows, though one large symbol - emblazoned across the front of the breastplate - still gives off a faint blue light.
This symbol is the particular pattern of the stylized double eye, eight spheres connected with two at the center. It is the symbol of the Lost Radiants, back when they'd been called the Knights Radiant.
The Shardbearer asks Dalinar who trained him in the sword. He then tells him that his stances are unfamiliar to him, but that they were practiced and precise, and that this level of skill comes only with years of training. He says that he has rarely seen a man - knight or soldier - fight as well as Dalinar did.
He then tells Dalinar that should he wish to put his mysterious training to use, that he should come to Urithiru. He says that he can't promise Dalinar a position in one of the orders because that decision doesn't belong to him. But, if Dalinar's skill with the sword is similar to his skill with hearth-tending implements, then he is confident that Dalinar will find a place with the Radiants.
The blue knight's armor then begins to glow faintly, and he launches into the air, as if falling straight up. Dalinar stumbles back, shocked, watching the glowing blue figure rise, then arc downward toward the village.
In the same vision as above, yet after the male Shardbearer's attack on the monsters, this woman in delicate Shardplate tells Dalinar (again, as Heb) to be at peace, then kneels beside him holding something bright. It is a topaz entwined with a heliodor, both set into a fine metal framework, each stone as big as a man's hand. She has light tan eyes that almost seem to glow in the night, and she wears no helm. Her hair is pulled back into a bun. She raises a hand and touches his forehead.
Ice washes across Dalinar and suddenly, his pain is gone. The woman reaches out, touches Taffa (Heb's wife), and the flesh on her side regrows in an eyeblink. Her skin knits up over muscle without flaw, and the female Shardbearer wipes away the blood and torn flesh with a white cloth.
The female Shardbearer then stands; her armor glows with an even amber light. She smiles and turns to the side, a Shardblade forming from mist into her hand as she rushes to aid her companion.
As Dalinar watches, one of the monsters lands a scraping hit on the Shardbearer in blue, and he realizes that the danger to these Shardbearers is real. The female Shardbearer turns to him, with her helm on. She seems shocked as Dalinar throws himself at one of the black beasts, slashing it with his poker.
Dalinar falls into Smokestance and fends against the beast's counterattack. The female Shardbearer turns to her companion, then the two of them fall into stances forming a triangle with Dalinar. With two Shardbearers alongside him, the fighting goes remarkably better than it had previously. He only manages to dispatch a single beast, but he fights defensively, trying to distract and keep pressure off the Shardbearers. The creatures do not retreat. They continue to attack until the last one is sliced in two by the female Shardbearer.