There are no exact records of the arms carried by the troops engaged at Sekigahara, but a general idea can be gained from the composition of a reinforcement sent to Ieyasu by Date Masamune in October 1600. Of a total of 3,000 men, 420 were mounted, probably carrying swords, 1,200 carried firearms, 850 carried spears, and 200 carried bows; there are no particulars for 330 men.
A similar contingent of some 2,000 men from another quarter included 270 mounted men, 700 men carrying firearms, 550 carrying spears, and 250 carrying bows; there are no particulars for the rest. These and other records show that by 1600 the most important weapons were firearms, followed by spears and next by bows. Swords came last.
So there you have it: katana look nice, but ask those who were in the know and they'd always have gone for trusty old yari, and they liked teppo best of all.
Actual matchlock firearms were only introduced to Japan by the Portuguese in about 1540, so it was only in the course of 60 years that they came to surpass the bow in terms of importance. Almost like with the Maori musket wars, a foreign technology was introduced which totally revolutionised Japanese warfare and changed social mores indelibly (though in this case, in the opposite direction to that of the Maori: Japan became more conservative and backward as a consequence). This is a lesson for any DM who is interested in creating a living, breathing, sort of a world: imagine what could happen to an orc society once firearms (or a certain type of magic) is introduced.
But I'm more interested in spears. To put it simply, I'm a spear fan when it comes to D&D, and never create a fighter who doesn't have one (or a trident or similar). Swords don't interest me much: a spear is just as good in a fight - or better, because it lets you fight from a rear rank or from above/below - but it's also an invaluable tool: it's a 10' pole with a spike on the end. It's a trap-finding, hole-poking, enemy-tripping, depth-finding device extrordinaire which no self-respecting dungeoneer should leave home without. No wonder the medieval Japanese liked it so much.