And there I was thinking it had originated with Hell's Angels!
A quick search of "death before dishonour" brought up
https://knappily.com/ethics/sepukku-dea ... honour-276, so I stand corrected.
Right now I have no "willingness to die" but I understand the concept. To me it means having such a burning passion for a particular cause that I'd be prepared to die for it rather than recant. Due to a number of severe adverse events, I have a horror of torture. To me there's nothing worse than having another out-of-control person or persons deliberately hurting me, with no chance of escape and no time limit set.
It's not easy to be a passionate person with the knowledge that I can't defend myself from someone bent on hurting me; that I'm so attuned to violence that I miss clear warning signs. That probably accounts for me being a writer, these days a keyboard warrior. I get to have my say, often only to myself, but increasingly to people I'll never meet. Writing keeps me relatively sane and defines both Who I Am and What I Stand For.
I've noticed that "willingness to die" invariably hinges on a doubt-free belief in an afterlife in which one will be rewarded. Alternatively, one might live a "safe" life and be punished for actions arising from cowardice. That belief is present in every culture on earth to a greater or lesser degree, because without it the loss of people we love would be unbearable. That doesn't mean it's true.
I just googled "the saving lie" and there are a lot of scholarly references (books to buy!), so you might find what you're looking for in the abstracts.