Glory overcoming fear.
If you look at many of the writings of samarai(sp?), you see talk of, at the very least, dying to defeat your opponent(I saw this in another thread round here somewhere). This reflects something more deeply cultural than can be readily appreciated, but it is a way to combat fear. Many honor codes throughout the world were used specifically(sometimes explicitly) to mitiage natural behavior. For example, if it is considered a dishonour to be a coward, then one might avoid being a coward to avoid dishonour(or other negative stimuli). Look at cultures around the world for this- in Viking(again, sp?) culture, AFAIK, warriors who died in battle went to Vauhala, whereas those who did not did not receive so glorious a fate. I'm certainly not an expert on japanese culture of teh 14th,15th,16th centuries, but from what I've absorbed from popular culture, etc, it seems that honor was extremely important in this kind of culture. If to be dishonored is considered worse than death(or indeed in the case of dishonor great enough to force the bearer to commit seppuku[correct use of word?]), than why should you fear death in battle? What you fear more greatly is dishonor in battle- there is still fear, but it is no longer fear of death, it is fear of something different. May appear like you don't show any fear, but rather its just not showing fear of what is expected.