Kanaya(diamonds)Karkat: Ríastrad (Old Irish) Warp spasm, battle fury, a terrible mutation of the body and mind that Cú Chulainn fell into when excited by war
They learn early on that Karkat goes berserk when he is wounded. It's the two of them on LORAF doing quests, and an imp gets in a lucky shot. The resulting slaughter goes on until she can plant her open hand on his cheek. He comes back to himself slowly, pupils slowly returning to normal after having been blown out to paradox space, hands shaking from exertion and trembling fingers losing their grip on his sickle.
All she can think about is how scared she was when his eyes went wide and his pupils swallowed the grey of his irises. All he can think about is the searing red dripping down his arms, how his dirty little secret is on display. And he cringes away from her, smears the blood on his dark sweater and folds in on himself.
"Karkat…" she murmurs, reaching for him, "Karkat it's okay." He recoils from her touch; retreats two steps back for every step she takes forward. So she picks his sickle up from the ground, tries not to commit the look of shame and fear in his eyes to memory, and slices open the back of her hand. Unused as she is to the weapon, the wound is deeper than she intended, but she ignores it in favor of grabbing Karkat's hand.
His look of hope is painful, when she smears their two blood colors together in the palm of his hand. "Blood of my blood," she intones, and then plants a kiss on his forehead. "It'll be okay." And they clean themselves up and return to questing, like it never happened, save for a suddenly full diamond and a more careful approach to battle.
Except being careful does nothing to solve the root of the problem: Karkat's blood maddened rage. Because no matter how careful they are, the imps are more reckless, the bosses more powerful, and sometimes even just an accidental fall could draw enough blood to bring on his madness. Kanaya fears that it will get him killed, one of these days.
And eventually, it does. They were lucky to have been on his planet, having taken a break from frog breeding to do an on the run feelings jam. Needless to say it went badly, a cut too deep, a breathless snarl, and careless lunges forward with sickle primed for the reaping.
Until a fist smashed him into a lake, where he drowned.
She got him to his quest bed in time, barely. And as time would tell, even god tier didn't cure him of his battle madness, only made him more durable. She worried for him, worried for him so much her heart might as well jump from her chest and reside in his. "Blood of my blood," she whispered, once he returned to her with bright wings fluttering behind him.
"Blood of my blood," he responded, and kissed her forehead.