There are no wonder swords - just shit swords and good swords of most types.
The stuff about variable grade steels was used from Saxon/Viking times onwards in any decent sword. You simply cannot get the sharpness without brittleness otherwise. There were various methods, but for a decent sword something would be done. Guy called Oakeshot has published definitive books on swords and their manufacture if anyones genuinely interested in swords.
I collect swords, a good longsword (eg Gen 2 Black Prince) can do anything a katana can (eg the cutting bamboo standard tests it can do to the highest level with green or dry bamboo) - though its not quite as fast and well balanced since its heavier for use vs metal armour, against which a katana is useless (buy one and try it if you dont believe me). However vs non metal Katana is awesome.
Introduce this one as a matter of style but despite the mythology and the assertion of every culture that its sword was the best, its not really that different from any short sword from a waisted gladius on.