Disclaimer: neither Tristan nor the song are mine.

Challenge: "Animal I Have Become" by Three Days Grace.
Fandom: King Arthur

"So What if you can see
the darkest side of me?
No one will ever change this animal I have become"

It's always easiest on the battlefield for Tristan - out there things are simple. Kill or be killed; there's never time to think or feel, or thank the Gods, remember.
Killing people gets easier the more you do it, and Tristan has killed a lot of people, he realises when he lets himself think of those things. Go for the heart, and if you can't get a shot at that then the throat is the next best option. Of course there are other ways and means to snuff out a life, but sometimes they're messy and washing out the blood from his hands and hauburk takes longer.
Swords don't scare him. He's torn out arrows from his own flesh and faced off enough Woads with a detachment that has had even Galahad telling him that he's a suicidal idiot.
Death is always there – a black eyed minx who is always close enough to touch but never near enough to embrace.
And that's alright.
While he lives he can protect the others. Can see a future for them.
But sometimes it's hard looking at his reflection in the water. A long time ago he was someone's son. He was a boy. Not a wolf chained to Rome. Once he was clean.
The blood from his hands clouds the water and when he throws it away he is careful not to contaminate the river that runs sweet and clear beside Hadrians Wall.

He might be ruined, but the water that runs to the ocean far away where his family remember him as the skin he has long since shed, will at least be pure.