I'm reading the books of james clavell (shogun, tai-pan and gai-jin) and I've found references to a "last favour" or a "favour of the life" (probably it's not the exact translation as I'm reading the italian translation of the book). It should refer to a special kind of favour one person grants to another (the favourite son, the lover and son on) and when asked there will be no question about the motivation. This can be asked only one time in one's life and everything will be kept secret between the parts. Is this correct ? where can I find more about this topic ? or is this a fictional tradition ?