[@Obscene Symphony] 

Strangely enough, this has actually been asked quite frequently in the past. Sensations are briefly (and inadequately) touched on in the character sheets section.

The [i]sensation[/i] your character represents is less of a "Seven Deadly Sins" vibe and more of a "this is what first inspired me to fight" vibe. It's something that your character feels deep within themselves, a part of who they are and a part of their history, something they call back on and remember when they feel the urge to fight.

Sorry, that too was confusing and inadequate. 

Let me say it this way:

Your character, when he/she was young, tasted their own blood when their guts were spilled by some bad robber dude. 
Strangely enough, they remember this.

They live the rest of their life up until warbrand. This sensation is ingrained as a part of them. (It's not necessarily a trauma thing, but it's the easiest to be interesting/establish/explain). They think about it. They dwell on it.

When War calls upon them to take up their warbrand, they accept, [i]very likely fully knowing what these Warriors have been doing in the city[/i]. The sensation becomes a part of their reason to fight, or a part of their internal conflict, or a part of who they are as a person post-"War". [b]It is up to you how this sensation manifests in your character, but I would highly recommend reflecting it in at least one, or maybe more, ways.[/b]

Anyway, hope that helped~!
If you need more examples, I can analyze my own character and spot out where I reflect him having Instinct.
<3

-crabs