@thatguythere That is pretty much the idea. Though on the sliiiiiiightly more (and less, let's be real here, I'm talking about soundtrack fodder) 'no, I'm not completely kidding' front, I kinda hate justifications (which strike me as being more like a standard montage writeup), but like the idea of a 'montage theme song'. It's a little more about mood and mindset and, well, vibe. Which is a little more what helps build a character than a laundry list of how many pounds of sand they pounded or how many wooden posts they kicked, and so on.
The justification approach I would liken to 'write a chronological background'.
The 'come up with a themesong for your wacky montage' thing I'd liken to 'write up your general character concept'.
One's more about the journalistic 'who, when, where, what, why', and the other is more about feel and personality.
I'd never stop someone from writing a traditional background or justification if they wanted to do that for their own reference and it fits the way they process things about their character better, and it'd probably get the same perk (if any) as the vibe approach, but I get a better idea of what the character went through or how they felt about it, how it changed them, etc. from something a little more evocative and abstract. It may be weird, but I'm strangely OK with that.