"A time when you showed mercy..."
I could re-tell about how instead of sating myself with an overly curious mana wyrm - during Quel'thalas' early days in alliance with the Horde - I instead formed a bond with the little creature and kept it as a companion ever since.
But choosing not to feed is not mercy, even if it is self-denial for another's sake.
Mercy was when I held the sobbing, shuddering, blank-eyed shell of someone I knew who had gone Wretched in my arms. I let the Farstiders and other arcanists I was with clean up the more violent ones in the hive without batting an eyelash. They were insane, they'd been through too much, never finding the balance between withdrawal from magic and glutting on it - their minds had become as unstable as their bodies, spiraling out of control. Of course they were violent, of course they would attack.
But not her. She was weak, scared, disoriented, and with no end to her pain.
I stepped in, told the others to go away, leave me alone with her. I tried saying a few gentle things as I held her, shaking on the floor. Tried to get through the mana-haze to the person I knew. Her recognition of me was broken, like everything else about her.
I softly sang a stupid little tune we'd made up as apprentices to her, rocking her. I listened to her start trying to hum along, latching onto that familiarity unconsciously.
And then I took her head gently in my hands and shot pulse after pulse of arcane into her skull.
That was mercy.
A/N - Originally done as a meme on tumblr. The meme was to ask about the different aspects of a character who's killed before, and how it made them feel, impacted their lives, etc. Musing-Zero asked the option about a time when mercy was shown. Instead of going the obvious route for mercy by making it about a time when Aranya spared a life she could or should have taken, I went the more challenging route of making the kill itself an act of mercy, by putting her Wretched friend out of her misery.